UNITED NATIONS (CNN) -- A top U.N. human rights official accused Syria Thursday of engaging in crimes against humanity.
"They are both widespread and they are being committed in a systematic manner," said Ivan Simonovic, assistant secretary-general of the Office of the High Commissioner for Human Rights.
The situation, in at least parts of Syria, "has reached the threshold to be considered as an internal armed conflict," or civil war, he told CNNI's "Amanpour."
"From (an) international legal perspective, that means that, a part of crimes against humanity, there might be commission of war crimes as well."
Simonovic said members of a U.N. mission returned last week from the region. Though denied entrance to Syria, they interviewed witnesses in neighboring countries and learned that "the crimes are continuing," he said. "There is unselective shelling, there is deliberate targeting with live munition of protesters, there is systematic torture going on in prisons, and this is the torture of the worst possible form."
Simonovic added, "It includes physical torture as well as psychological threats -- threats such as raping members of family, direct torture involving putting people in the unnatural positions for a long time, torturing them by burning them, and so on and so on ... it's appalling."
He said his office was calling on "all sides" to stop the violence and for the government to release arbitrarily detained persons, as called for the by the six-point peace plan of joint U.N.-Arab League Special Envoy Kofi Annan. "But this is not happening yet," he said. Though about 200 detainees have been released, thousands more remain in custody, he said. "For some of them, we cannot establish their whereabouts."
Simonovic's remarks came as diplomats were meeting at the United Nations to discuss how to proceed on Syria.
"It has been sort of Syria Day as far as we're concerned," Secretary-General Ban Ki-moon told reporters outside the Security Council after emerging from 10 hours of talks that concluded that the situation continues to deteriorate.
"How many more times have we to condemn them and how many ways must we say we are outraged?" he asked. "The danger of full-scale civil war is imminent and real, with catastrophic consequences for Syria and the region."
He noted "little evidence" that the regime is complying with its commitment under the Annan plan, which was endorsed by the council more than two months ago, and said the opposition "is hardening and turning increasingly to arms."
According to the London-based Syrian Observatory for Human Rights, 2,747 Syrians were killed between April 12, when the Annan plan was put in place, and June 5. The dead included 1,784 civilians, 859 members of the Syrian military and 104 defectors, it said.
Ban said the killing witnessed in recent weeks "is indicative of a pattern that may amount to crimes against humanity. The confrontations in certain areas of the country have taken on the character of an internal conflict subject to international humanitarian law and possible war crimes prosecution."
Though Ban said the Annan plan "remains at the center of our efforts," the secretary-general said a planned June 20 summit in Los Cabos, Mexico, could aid discussions on how to proceed.
He added that he would present the Security Council with several options. "It is up to the members of the council to find common course," he said.
Arab League Secretary-General Nabil el-Araby and Annan also addressed the world body. El-Araby called for "all kinds of pressure" short of the use of force to be applied to Damascus. "Enough is enough," he said. "We cannot accept any more killing of innocent people."
Asked about the characterization by some observers of his plan as "dead," Annan said, "I'm not sure whether it is the plan that is dead or it is implementation that is lacking."
He added, "You could say we are drifting, if we are not already in, a sort of a civil war. All efforts are being made that, if it were to become a full-blown civil war, it doesn't spread to neighbors."
Asked whether he envisions a political solution that could leave Syrian President Bashar al-Assad in power, Anann said, "The Syrian people will have to decide their future."
The council members said they had concurred that, despite progress on it, the Annan plan remains their best hope for a solution.
But U.S. Ambassador Susan Rice said that the council needed to "come together and apply pressure and impose consequences for the noncompliance of the Syrian regime."
France's Charge d'Affaires Martin Briens said his country will host the next meeting of the "Friends of Syria" on July 6. The group has embraced calls to pressure the regime.
But China's ambassador, Li Baodong, reiterated that his country opposes military intervention. "We believe it is very important to push for political mediation," he told reporters.
Russia's ambassador, Yuri Churkin, described as "counterproductive" the decision by opposition groups inside Syria not to observe the Annan plan if the Syrian government was not going to do so too. During just two days -- on June 3 and 4 -- 80 people on the side of the government were killed by the opposition in Syria, he said. "This is not a kind of violence level against government where you can realistically hope for serious restraint on the part of anybody," he said.
He said discussions were under way to hold an international conference on Syria. "I hope that this initiative will proceed without delay," he said.
China and Russia, allies of al-Assad, have stressed their opposition to outside interference in Syria while continuing to back Annan's plan. As permanent Security Council members, the two nations have used their veto powers to block draft resolutions against the regime.
The United States plans to send a delegation to Russia this week to press for tough action against the Syrian regime, a senior State Department official said.
The difficulty faced by U.N. observers in Syria was underscored Thursday by small-arms fire that targeted a group of them as they tried to get to the scene of yet another massacre, Ban said earlier Thursday.
No one was hit, said a spokeswoman for Maj. Gen. Robert Mood, head of the U.N. Supervision Mission in Syria.
The latest massacre occurred on Wednesday in the village of Qubeir, west of Hama, and included reports that dozens of civilians, including women and children, were killed.
Mood said observers heading to the village to verify reports of the killings had been blocked by soldiers and civilians. Residents told observers they would be at risk if they were to enter the village.
"Despite these challenges, the observers are still working to get into the village to try to establish the facts on the ground," Mood said. "UNSMIS is concerned about the restriction imposed on its movement as it will impede our ability to monitor, observe and report."
The incident was one of several that the observers have had to contend with, said Britain's Ambassador Mark Lyall Grant.
"Now in those circumstances, it's clear that the current configuration of the mission is not sustainable in the long term and so I think it's our duty, it's our moral duty, to consider what other options there will be going forward," he said.
The U.N. meeting occurred in the wake of the killings in Qubeir and, two weeks ago, in Houla. More than 100 people, including women and children, were killed in Houla. Opposition activists blamed government forces and allied militia, an assertion denied by al-Assad.
"Those responsible for perpetrating these crimes must be held to account," Annan said. "We cannot allow mass killing to become part of everyday reality in Syria."
He said he had urged al-Assad in a meeting in Damascus last week to "change his military posture and honor his commitments to the six-point plan."
But al-Assad "believed the main obstacle was the actions of militants," Annan said. "Clearly, all parties must cease violence. But equally clearly, the first responsibility lies with the government."
Though Syria has released some detainees and there has been agreement "on modalities for humanitarian assistance," more is required, Annan said.
Since he and al-Assad spoke, "shelling of cities has intensified" and "government-backed militia has free rein with appalling consequences."
Annan said armed opposition forces haven't seen a "reason to respect cessation of hostilities" and "have intensified their attacks." Referring to bombings in Damascus and Aleppo, he said the situation is "made more complex" by attacks that are "indicative of the presence of a third actor." Some analysts say jihadist groups are responsible for those acts.
Syrian Ambassador to the U.N. Bashar Jaafari reiterated that anti-government terrorists, and not the regime, are responsible for the bloodshed. The government said terrorists timed the latest massacre to coincide with the U.N. meetings in order to make the regime look bad.
He added that Syria "is ready to receive an investigation committee from neutral countries that respect the U.N. charter and reject any intervention in the Syrian affairs," according to the government's Syrian Arab News Agency.
Jaafari said Syria is open to reform and to dialogue, and that it has no problem with the opposition. However, he said, some opposition forces composed of outside elements are taking up arms and have no desire for reconciliation.
Opposition activists accuse forces loyal to al-Assad of the killings at Qubeir, and they placed the number of dead at 78.
Regime forces shelled Qubeir before militias used knives, guns and AK-47 rifles to kill residents, the opposition Local Coordination Committees of Syria said.
About 40 victims of the attack were buried in a mass grave Thursday, according to a youth activist whom CNN is not naming for safety reasons. Shabiha -- or pro-government gangs -- took other bodies to neighboring villages, the activist said.
More than half of those killed were women and children, said a local activist who reported having carried bodies.
CNN cannot independently confirm reports from within Syria because the government limits access by international journalists.
The recent violence has revived calls to isolate the regime and toughen sanctions.
U.S. Secretary of State Hillary Clinton, meeting Thursday in Istanbul with Turkish Foreign Minister Ahmet Davutoglu, called the latest violence "simply unconscionable." She reiterated the U.S. stance that al-Assad must go and the international community must unite around a plan for Syria after al-Assad.
Clinton said it is important to give Annan's peace initiative "the last amount of support we can muster."
Davutoglu, whose country has been critical of the al-Assad regime's actions, said all members of the U.N. Security Council must work together to stop the regime's actions.
At least 15 people were killed Thursday in Syria, the Local Coordination Committees of Syria said.
The United Nations for months has said more than 9,000 people have died in Syria. But death counts from opposition groups range from more than 12,000 to more than 14,000. Tens of thousands of people have been displaced.
CNN's Richard Roth, Joe Vaccarello, Salma Abdelaziz and Faith Karimi contributed to this report.