The Obama administration closed the U.S. embassy in Damascus on Monday and pulled all American diplomats out of violence-wracked Syria as the U.S. stepped up pressure on President Bashar al-Assad to leave power.

Robert Ford, the American ambassador, and 17 other U.S. officials left Syria and were expected to travel back to the United States. Ford informed Syrian authorities of the decision to leave earlier in the day, State Department officials said. Two diplomats left by air and the others went overland to Jordan.

Their departure came two weeks after the State Department warned that it would close the embassy unless Assad's government better protected the mission, citing safety concerns about embassy personnel and a recent series of car bombs. And it coincides with a U.S. effort to build an international coalition in support of Syria's opposition.

Syrian troops were accused Monday by human rights activists of shelling homes and a makeshift hospital, killing at least 17 people.

Also Monday, U.K. Foreign Secretary William Hague announced that the British ambassador to Syria had been recalled for "consultations." As well, he told parliament, the British government will "review all options" regarding its embassy in Damascus. He said there are advantages in keeping an embassy open there to stay in better touch with events in the Middle East.

In Washington, State Department spokeswoman Victoria Nuland said in a statement that Ford remains the U.S. ambassador "to Syria and its people," and said he would continue his work on Syria, maintaining contacts with the Syrian opposition and supporting "the peaceful political transition which the Syrian people have so bravely sought."

'Not every situation is going to allow for the kind of military solution we saw with Libya.'—U.S. President Barack Obama

The UN estimates that well over 5,400 people have been killed since March, when mostly peaceful protesters rose up to voice their anger toward four decades of dictatorship by the Assad family. A brutal crackdown ensued, prompting armed rebels to take the fight to regime troops and try to establish control in pro-opposition areas. The government has responded with even more violence, raising fears of an all-out civil war.

Despite the increased bloodshed, world powers are bitterly divided over how to deal with the situation. The U.S., its European partners and much of the Arab world want Assad to step down and transfer power to his vice president as part of a transition to democracy. But Russia and China, wary after watching the West help Libyan militia oust Moammar Gadhafi, reject any talk of military intervention or regime change. They vetoed a UN resolution over the weekend that would have endorsed an Arab League plan for Syria's post-Assad future.

Obama defends U.S. handling of conflict

U.S. President Barack Obama said the ongoing conflict in Syria should be resolved without outside military intervention, saying a negotiated solution in Syria is still possible. And he defended his administration's actions during the 11-month uprising against Assad's regime.

"We have been relentless in sending a message that it is time for Assad to go," Obama said during an interview with NBC. "This is not going to be a matter of if, it's going to be a matter of when."

Obama deflected questions about whether the U.S and its partners should intervene militarily in Syria as they did in Libya, saying those decisions are made on a case-by-case basis.

"Not every situation is going to allow for the kind of military solution we saw with Libya," he said. "I think it is very possible for us to try to resolve this without recourse to outside military intervention."

With diplomacy at an impasse, U.S. Secretary of State Hillary Rodham Clinton called Sunday for "friends of democratic Syria" to unite and rally against Assad's regime, previewing the possible formation of a group of like-minded nations to co-ordinate assistance to the Syrian opposition. Speaking in Bulgaria, she said the world had a duty to halt the violence and see Assad out of power. She called the UN setback a "travesty."

The contact group is likely to be similar, but not identical, to the one established last year for Libya, which oversaw the international help for Gadhafi's opponents. It also co-ordinated NATO military operations to protect Libyan civilians, something that is not envisioned in Syria.

The Syrian group is likely to concentrate on enhancing sanctions against the Assad regime and trying to bring disparate Syrian opposition groups inside and outside the country together so that they can form a more formidable opposition. It could also seek more humanitarian relief for embattled Syrian communities and greater monitoring arms sales to Assad's government.

Call for consensus at Security Council

In an unusually strong statement Monday, General Assembly President Nassir Abdulaziz Al-Nasser reiterated the urgent calls of the Arab League and international community for Syrian authorities to immediately end the killings and halt human rights violations.

Al-Nasser, who is from Qatar, warned that "the longer the Security Council remains divided in adopting a consensus position on developments in Syria the more difficult the situation becomes, with more Syrians being killed daily."

Earlier Monday, UN Ambassador Susan Rice said China and Russia were running the risk of suffering the same sort of international isolation as Assad because of their decision to block a UN Security Council vote embracing an Arab League solution for the Syrian crisis.

Rice said she thinks both Moscow and Beijing "will come to regret" their votes Saturday against the Arab League-sponsored resolution aimed at moving Assad in the direction of a peaceful transition to democracy in his violence-wracked country.

The Obama administration has long called on Assad to leave power, and officials insist his regime's demise is inevitable.

After the UN veto, the commander of the rebel Free Syrian Army, Col. Riad al-Asaad, said "there is no other road" except military action to topple Assad.

With files from The Associated Press