Watch Anderson Cooper's exclusive interview with Sen. John McCain on Wednesday's "AC360," on CNN 8 p.m. and 10 p.m. ET. Read a version of this story in Arabic.
Beirut, Lebanon (CNN) -- Qusayr has been bombarded for more than a week.
The shelling of the town of 20,000 civilians in Syria, just across the border from Lebanon, has been so intense that residents wait for the occasional lulls at night to bury the dead.
Activists say the town is encircled by members of Hezbollah, the Shiite Lebanese militant group intent on helping the regime of Syrian President Bashar al-Assad.
Qusayr is a key location because it sits astride one route to the Syrian coast and another to the Lebanese border. For the rebels, holding Qusayr is important because it's another way of strangling the regime's ability to sustain itself, and it complicates Hezbollah's access to Syria.
The wounded are packed into the basements of ordinary homes, where Dr. Qasim al-Zayn and others do what they can.
But it's impossible work. Sometimes a wounded limb can't be treated, so instead it must be cut off.
"We have to amputate most of the time as we are unable to reconnect the arteries due to the high number of casualties," al-Zayn told CNN via Skype.
He fears a massacre in the city, and reports four instances of chemicals being deployed there that caused breathing difficulties.
But most of the people being treated in the basements that serve as operating rooms in Qusayr are victims of shelling and snipers.
For some of the children who've endured the two years of conflict, this latest onslaught has proven too much.
"The psychological states of children are terrible -- fear, terror, wetting themselves, loss of balance, hyperactivity," al-Zayn said. "They will either be wounded, die, or go crazy."
In these conditions, he said, some would welcome death.
"Just before I came here I was treating a casualty who lost a lot of blood and arrived to us barely with a pulse," al-Zayn said. "We operated on him, and he is unconscious."
Though his friends have been blowing into his breathing tube for three days to keep him alive -- "We've run out of oxygen," al-Zayn said -- they're not sure keeping him alive is the best thing.
"We've started wishing some casualties die just to limit their suffering," the doctor said.
Abulhoda al-Homsi, a rebel activist, told CNN that at least 10 airstrikes followed by artillery and mortar fire had hit Qusayr as well as the nearby villages of Dabaa and Hamidiya.
The state-run Syrian Arab News Agency said the fighting was part of its mission "to pursue terrorists in Qusayr and its countryside" and that the military had seized control of the Dabaa Airport.
The activist disputed that account, saying rebels maintained control of the airport.
On Saturday, Hezbollah leader Hassan Nasrallah acknowledged that his fighters were in Qusayr. "Our men are there and we will make victory there," he said in a televised address that was broadcast in Lebanon.
Salim Idriss, a general with the rebel Free Syrian Army, said Wednesday that his forces were outgunned by Hezbollah fighters and appealed to the international community for heavy weapons to help his fighters in Qusayr.
"We just have light weapons," he said on CNN's "Amanpour." "They are surrounded and we are afraid that Hezbollah will make a big massacre there."
Still, he said, whatever happens, "I promise Hassan Nasrallah he will not have a victory in Syria."
On Monday, Idriss accompanied U.S. Sen. John McCain in and out of Syria. The Arizona Republican is the highest-ranking U.S. official to visit during the war.
In an exclusive interview to air on CNN's "AC360," McCain told Anderson Cooper that the U.S. State Department had been "very cooperative and helpful" in supporting his unannounced visit, and that "many Syrians" showed their bravery by helping out as well.
"I wanted to be able to go back and tell my colleagues in the Senate that at least the military side of those fighting against Bashar Assad is well-organized and well-led," he said.
McCain met with 18 commanders of the rebel Free Syrian Army near the country's northern border.
"Their message was, to be frank with you, they do not understand why we won't help them," McCain said.
While many countries -- including the United States, France and Britain -- have called for al-Assad to step down, they have not agreed on whether to arm Syrian rebels.
One concern has been that radical Islamic militants such as members of al-Nusra Front have joined the rebels in their fight. The United States has designated al-Nusra Front as a pro-al Qaeda terrorist group.
But McCain said members of the extremist group represent only 7% of the nation's rebel forces, who number 100,000. "We can help the right people," he said. "Is there some risk involved? Absolutely. But is the status quo acceptable?"
He said that status quo has destabilized not only Lebanon but Jordan, where hundreds of thousands of Syrians have sought refuge. "If this conflict continues, it is bound to spill over into the region; we're in real danger of a Mideast in great turmoil," he said.
In addition to facing a shortage of weapons, the opposition is undermined by disunity. After a chaotic week of meetings in Istanbul, Syria's rebel National Coalition got a failing grade from some of its members.
"This leadership failed in all tests: organizational, political and humanitarian," said the Local Coordination Committees of Syria and several other groups in a statement. "The coalition, based on its current organizational structure, is impotent to carry out the duties entrusted to them because of the negative inter-political bickering between the various groups and members."
As the people of Qusayr were suffering, officials in foreign capitals were mulling Hezbollah's effort to support the al-Assad regime.
"The conflict in Syria is spinning out of control," U.N. High Commissioner for Human Rights Navi Pillay said at a meeting of the U.N. Human Rights Council in Geneva, Switzerland.
"The increasing number of foreign fighters crossing Syria's borders to support one side or the other is further fueling the sectarian violence, and the situation is beginning to show worrying signs of destabilizing the region as a whole."
The solution to Qusayr must be political, she said. "It will not be military."
Russia's state-run Russia Today news channel cited Foreign Minister Sergey Lavrov as saying that Hezbollah fighters were in Syria to protect the Shia population and holy sites from the threat posed by Sunni rebel forces.
Questions on chemical weapons
Meanwhile, questions about the possible use of chemical weapons by the al-Assad regime continued to be raised.
A spokeswoman for the British Foreign and Commonwealth Office told CNN that the British ambassador wrote last week to U.N. Secretary-General Ban Ki-moon "with additional information about (allegations of) chemical weapons use in Syria."
The spokeswoman would not elaborate.
Another Western official said the information was related to three incidents near Damascus in March and April.
U.S. Ambassador to the United Nations Susan Rice told reporters, "We continue to be in communication with the U.N. team that is to investigate the use -- or the potential use -- of chemical weapons."
But, she said, the Syrians' refusal to allow give unlimited access to an investigative team has stalled the investigation.
Missiles from Syria hit Lebanon
On Wednesday, three missiles fired from Syria landed in woodlands near the Lebanese town of Hermel, a Hezbollah stronghold, Lebanon's state news agency NNA reported. It did not report any injuries.
On Tuesday, two rockets fired from Syria landed in and near Hermel, it said. No one was hurt.
It was not immediately known who fired the rockets.
Also Tuesday, three Lebanese soldiers were killed when unknown armed men opened fire at a military checkpoint near Lebanon's border with Syria, according to NNA.
European Union to lift embargo on rebels
The European Union voted Monday to lift its embargo on arming Syrian rebels effective in August, in a move that British Foreign Secretary William Hague said was intended to pressure al-Assad to negotiate.
"It was important for Europe to send a clear signal to the Assad regime that it has to negotiate seriously, and that all options remain on the table if it refuses to do so," Hague said.
But UNHCR's Pillay was unswayed. "The message from all of us should be the same: We will not support this conflict with arms, ammunition, politics or religion," she said in a statement.
A statement posted Tuesday on the state-run Syrian Arab News Agency and attributed only to a spokesperson for the Foreign and Expatriates Ministry blasted the move.
"The recent EU decision exposes the falsity of their allegations and it proves they are hindering the international efforts aimed at contributing to achieving a political settlement to the crisis in Syria based on national dialogue among the Syrians led by Syria," the statement said.
Russia's deputy foreign minister slammed the EU decision, saying that arming the rebels would undermine the peace process.
Russia said it would move ahead with plans to ship S-300 surface-to-air missiles to the Syrian government, contending that doing so may help contain the conflict.
CNN's Tom Watkins, Amir Ahmed, Saad Abedine and Tim Lister contributed to this report