(CNN) -- Syrian President Bashar al-Assad must order a cease-fire immediately under a peace plan Syria accepted and not await concessions from the opposition, a spokesman for special envoy Kofi Annan said Friday.
"The government must stop first and then discuss a cessation of hostilities with the other side and with the mediator," said Ahmad Fawzi, Annan's spokesman. "We expect him to implement this plan immediately."
Annan is making plans to travel to Iran to discuss the Syrian crisis.
The United States also insists the al-Assad regime halt the violence first, followed by the armed opposition's laying down its arms.
Explaining how this would work, a senior State Department official said Friday: "Get the guns silenced and then, as Assad takes steps to implement promises he made, then Kofi Annan and others with influence with the opposition would make sure that their guns should be silenced as well."
Meanwhile, U.S. Secretary of State Hillary Clinton arrived Friday in Saudi Arabia for discussions with King Abdullah and leaders of other Gulf states before heading to Turkey over the weekend for a meeting of the 60-nation Friends of the Syrian People group.
At her first stop Friday in Riyadh, Clinton briefed Abdullah and Foreign Minister Saud al-Faisal. "My understanding is that the conversation on Syria focused on the full range of agenda items that we have for the Friends of Syrian People," a senior State Department official told reporters. Those items include getting humanitarian aid to the Syrians; tightening sanctions and implementing those that already exist; cataloging atrocities; and offering support for the opposition, the official said.
A Syrian opposition group, the Syrian National Council, is scheduled to make a presentation to the meeting in Istanbul summarizing its efforts to unite the disparate groups that form the opposition. U.S. administration officials have expressed concern over their lack of cohesion and are urging them to lay out a plan for a post al-Assad Syria that would protect ethnic and religious groups.
"We are continuing to work with them to try to strengthen them in that regard," the official told journalists. "They have been reporting that they expect to be able to make progress and to demonstrate progress at this meeting on Sunday, so we'll look forward to what they bring."
Also Friday, the United States sanctioned three senior Syrian officials in al-Assad's regime.
Dawood Rajiha, Syria's defense minister; Munir Adanov, a senior Syrian army official; and Zuhayr Shalish, the head of presidential security, were targeted in the action announced by the Treasury Department.
The United States, along with many other Western governments, has repeatedly called for al-Assad to step down, but has been stymied by Russian and Chinese opposition in the U.N. Security Council.
The sanctions prohibit U.S. citizens from engaging in any business or transaction with the three officials and freeze any assets they may have in U.S. jurisdictions.
The six countries in the Gulf Cooperation Council have closed their Syrian embassies and called on the international community to work more aggressively to stop the bloodshed.
Plans for the weekend meeting were under way as the state-run Syrian Arab News Agency reported that Foreign and Expatriates Ministry spokesman Jihad Maqdisi told Syrian TV that "the battle to topple the state in Syria is over, and that the battle to solidify stability, rally visions behind the reform process, prevent those who seek to sabotage reform, and move on toward a renewed Syria has begun."
But opposition activists gave no indication that they agreed with that assessment. They reported heavy fighting and shelling throughout Syria on Friday. At least 45 people, including four children and two women, were killed, said the Local Coordination Committees, a network of activists in Syria.
The fresh fighting cast more doubt on the peace plan brokered by Annan, the United Nations and Arab League joint envoy to Syria. Al-Assad accepted the terms of the plan Tuesday, but violence has persisted.
The United Nations estimates that the Syrian conflict has killed more than 9,000 people since a government crackdown on protesters began in March 2011. Opposition activists put the toll at more than 10,000.
CNN cannot independently confirm reports from inside Syria because the government severely restricts access by international journalists.
The peace plan calls for an end to the violence by the government and opposition, timely humanitarian aid, the release of arbitrarily detained people, freedom of movement for journalists, and respect for peaceful demonstrations and freedom of association.
Syria routinely blames armed terrorist groups for violence in the country, but most reports from inside the nation suggest that the government is slaughtering civilians to quash dissent.
"In return for a formal commitment by Syria for the success of Annan's mission, it is necessary for him to obtain commitments from other parties to stop all terrorist acts, disarm gunmen and to end their terrorist acts, kidnapping, killing innocents and sabotaging infrastructure," al-Assad said, according to the Syrian Arab News Agency.
He expressed hope that Annan will deal with the crisis, saying Syria is willing to conduct a national dialogue with groups seeking stability.
Annan, a former U.N. secretary-general, plans to be in Istanbul this weekend to attend the second meeting of the Friends of the Syrian People. He intends to brief the U.N. Security Council in a private meeting Monday.
Turkish Prime Minister Recep Tayyip Erdogan called for Tehran to cooperate with Anakara in resolving the Syrian crisis. "Iran and Turkey should launch joint cooperation and help each other in this regard," he said, according to the Iranian semiofficial Fars News Agency.
At the meeting in Istanbul, Turkey plans to renew a call for international help in dealing with the soaring numbers of Syrians fleeing to Turkey's southern provinces.
CNN's Jill Dougherty, Amir Ahmed, Joe Sterling, Tracy Douiery, Richard Roth and Gavino Garay contributed to this report.