WASHINGTON - 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 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 comes 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. 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." Syria forces keep pounding Homs; 33 dead Rice: Russia siding with dictator over people U.S. floats coalition against Syria Syrian officials pushed back at the notion that they hadn't done enough to ensure Embassy security. The U.N. 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 Muammar Qaddafi, reject any talk of military intervention or regime change. They vetoed a U.N. resolution over the weekend that would have endorsed an Arab League plan for Syria's post-Assad future. Clinton calls for united front against Assad Russia, China veto UN resolution against Syria 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," Mr. 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. Mr. 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, 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 coordinate 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 U.N. 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 Qaddafi's opponents. It also coordinated 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. Appearing on "CBS This Morning" earlier Monday, U.N. 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 U.N. Security Council vote embracing an Arab League solution for the Syrian crisis. Watch video at left. 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. But just over a year ago, the administration had sought to engage Damascus and sent Ford to the country in the hopes of prying away Iran's main ally in the Arab world and gaining a more willing partner in American efforts to forge stability in Lebanon and peace among Israel and its Arab neighbors. Syria had gone years without an American ambassador after the Bush administration broke ties over Syria's alleged role in the 2005 assassination of politician Rafik Hariri in neighboring Lebanon, and it remains on a U.S. "state sponsor of terrorism" list. Assad largely shrugged off U.S. attempts to pull his nation away from its alliances with Iran, Hamas and Hezbollah. And as protests escalated in Syria, Ford took on an increasingly high-profile role defending the rights of Syrian protesters. Threats led the U.S. to pull him out of the country in October, but he returned in December to what officials described as an important job monitoring abuses and developments on the ground - even if U.S. engagement efforts were dead. To improve security, Washington wanted Assad's government to narrow a portion of the main Damascus thoroughfare that the embassy is located on so that its setback could be improved. The Syrians refused. The U.S. had sought to move the entire embassy elsewhere in Damascus for two decades, but has never received permission from authorities. Shutting the embassy and recalling American personnel is short of a complete break of diplomatic relations. A year ago the U.S. similarly closed its mission in Libya's capital as violence escalated, yet maintained for some time communications with senior Libyan officials as it sought to convince Qaddafi loyalists to abandon the regime and others to advance possible surrender scenarios. With Qaddafi's death last year, the revolutions that toppled decades-long leaders Hosni Mubarak in Egypt and Zine El-Abidine Ben Ali in Tunisia, and Yemen's long-time strongman Ali Abdullah Saleh receiving medical care in the United States, Assad is among the Arab Spring autocrats left standing. His forces remain formidable and he continues to receive political - and possibly some military support - from Russia and China, but he has been unable to snuff out Syria's opposition. After the U.N. 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.