In the aftermath of Russia’s weekend election, the Obama administration said Monday that it would renew efforts to persuade Moscow to cooperate with international efforts against Syria.

“It is something that we expect to take up virtually immediately with the Russian side,” State Department spokeswoman Victoria Nuland said.

She suggested that Russia, which has vetoed two U.N. resolutions on Syria, had been “preoccupied” with its presidential election. In what appeared to be a coordinated message, British and French officials said much the same thing.

The appeals came as thousands of refugees crossed Syria’s borders into Lebanon, Turkey and Jordan to escape ongoing assaults by President Bashar al-Assad’s military forces.

Syria said it would permit the United Nations’ emergency relief coordinator, Valerie Amos, into Damascus for a two-day visit beginning Wednesday.

Humanitarian workers have been allowed access to parts of the city of Homs, the opposition stronghold that fell to government forces last week after a month-long artillery bombardment. But aid workers remain barred from the Bab Amr neighborhood, which bore the brunt of the attack.

As the United States and others continued to press Assad to allow humanitarian aid, Sen. John McCain (R-Ariz.) argued that such efforts have been overtaken by events on the ground. He called for the United States to organize and lead airstrikes to “protect key population centers” and establish “safe havens” in the northern areas from which opposition military forces could operate.

President Obama, McCain said in a speech on the Senate floor, “must state unequivocally that under no circumstances will Assad be allowed to finish what he has started . . . and that the United States is prepared to use the full weight of our air power.”

The senator said that U.S. willingness to intervene will spur “other countries to do the same.” Sens. Lindsey O. Graham (R-S.C.) and Joseph I. Lieberman (I-Conn.) later signed on to McCain’s statement, in a release Monday evening.

Although a number of primarily Republican lawmakers and GOP presidential candidates have called for tougher action by the administration on Syria, McCain went considerably further in urging airstrikes.

“There are always plenty of reasons not to do something,” he said. “We know the opposition is divided. We know the armed resistance inside the country lacks cohesion or command and control. We know that some elements of the opposition may sympathize with violent extremist ideologies or harbor dark thoughts of sectarian revenge. We know that many of Syria’s immediate neighbors remain cautious . . . and we know the American people are weary of conflict.”

Any air operations in Syria would require destruction of that country’s considerable air defenses, McCain acknowledged.

The administration has cited all those reasons in rejecting direct military intervention by the United States or other nations on the side of the opposition Free Syrian Army. Although McCain referred to U.S. and NATO bombing campaigns in the Balkans during the 1990s, and in Libya last year amid similar circumstances of civilian massacre, those operations were mandated by the United Nations or undertaken in cooperation with NATO.

During a visit to Washington last week, NATO Secretary General Anders Fogh Rasmussen reiterated the alliance’s determination not to become involved in Syria. And Russia’s veto has blocked U.N. approval even for demands that Assad step down.

Russian Prime Minister Vladi­mir Putin, who was reelected to the presidency Sunday, has given no indication that he would change his views or stop arms shipments to the Syrian government.

In a Twitter message Monday, Russian Deputy Foreign Minister Gennady Gatilov called for changes in a draft resolution being circulated at the U.N. Security Council demanding that Syrian forces stop attacks against civilians and allow access for aid workers.

Foreign Minister Sergei Lavrov is scheduled to meet Saturday in Cairo with his Arab counterparts.

Tunisia, Algeria, Egypt and other nations have rejected providing lethal aid to the Syrian opposition, but Saudi Arabia and other Persian Gulf countries have positioned themselves to begin arming the opposition forces.

“If the Syrian people want to defend themselves, is there something greater than the right to defend oneself and human rights?” Saudi Foreign Minister Saud al-Faisal said during a news conference Sunday.

At the United Nations, a spokeswoman for Amos said it was unclear whom she would meet with in Damascus or whether she would be permitted to view conditions in the most battered areas, including Homs.

Former U.N. secretary general Kofi Annan, who is serving as the joint U.N.-Arab League envoy on the Syrian crisis, will visit Damascus on Saturday as part of a high-level effort to negotiate a political deal ending the violence in the country.

Staff writer Colum Lynch at the United Nations contributed to this report.