A Turkish official also said his nation has held discussions with NATO allies, including the United States, on using Patriot missiles to protect a safe zone inside Syria.
The developments came within hours of President Barack Obama's re-election. U.S. allies anticipate a new, bolder approach from the American leader to end the deadlocked civil war that has killed more than 36,000 people since an uprising against Assad began in March 2011.
U.S. officials said Patriots or other assets could be deployed to Turkey's side of the border for defensive purposes against possible incursions, mortar strikes and the like.
But Washington isn't prepared to send any such equipment inside Syria, which would amount to a violation of sovereignty and a significant military escalation, said the officials, who spoke on condition of anonymity because they weren't authorized to speak publicly on the matter.
Like Britain, American officials are considering meeting with rebel military commanders. If the contacts were to happen, they would be most likely conducted by Robert Ford, the former U.S. ambassador in Damascus, who is currently in Doha for Syrian opposition talks, a U.S. official said. But no final decision has been made.
British Prime Minister David Cameron, visiting a camp for Syrian refugees in Jordan, said the U.S., Britain and other allies should do more to "shape the opposition" into a coherent force and open channels of communication directly with rebel military commanders.
Previously, Britain and the U.S. have acknowledged contacts only with exile groups and political opposition figures - some connected to rebel forces - inside Syria.
"There is an opportunity for Britain, for America, for Saudi Arabia, Jordan and like-minded allies to come together and try to help shape the opposition, outside Syria and inside Syria," Cameron said. "And try to help them achieve their goal, which is our goal of a Syria without Assad."
The foreign ministry official, who spoke on condition of anonymity in line with department policy, said discussions about the deployment of Patriot missiles to protect a safe zone had been put on hold until after the U.S. election.
Since the summer, Assad's regime has significantly increased its use of air power against rebels as government forces are stretched thin on multiple fronts.
The Turkish official said any missile deployment might happen under a "NATO umbrella," though NATO has insisted it will not intervene without a clear United Nations mandate.
"With the re-election of Obama, what you have is a strong confidence on the British side that the U.S. administration will be engaged more on Syria from the get-go," said Shashank Joshi, an analyst at London's Royal United Services Institute, a military and security think tank.
On the ground in Syria, rebels made a new push into the capital Wednesday. Opposition fighters fired mortar shells toward the presidential palace - but missed their target - and clashed heavily with troops in the suburbs of Damascus. The regime's capital stronghold has seen a surge in violence this week with some of the fiercest clashes in months.
The Britain-based Syrian Observatory for Human Rights and the Local Coordination Committees said the Syrian military was shelling another suburb, Beit Saham, with tanks and mortar shells, killing at least 18 people in that neighborhood alone.
In London, British Foreign Secretary William Hague said talks with rebel military leaders would not involve advice on military tactics or support for their operations. Hague also insisted that Britain would not consider offering weapons to Assad's opponents.
Face-to-face meetings with military figures will take place outside Syria, Hague said. Diplomats from the U.S., Britain, France and Turkey are already scheduled to meet with Syrian opposition groups Thursday in Doha, Qatar, though there has been no announcement that those talks will include discussions with rebel fighters.
He said British diplomats will tell rebel commanders to respect the human rights of captured Assad loyalists, amid concern over abuses carried out by both sides.
"In all contacts, my officials will stress the importance of respecting human rights and international human rights norms, rejecting extremism and terrorism, and working towards peaceful political transition," Hague told lawmakers.
At the Zaatari camp, which houses about 40,000 of the estimated 236,000 people who have fled into Jordan from Syria, Cameron said he would press Obama at the first opportunity to drive forward efforts to end the 19-month-old conflict.
Cameron plans to convene a meeting of Britain's National Security Council in London devoted entirely to Syria and discuss how the U.K. can encourage Obama to pursue a more direct strategy.
"Right here in Jordan I am hearing appalling stories about what has happened inside Syria, so one of the first things I want to talk to Barack about is how we must do more to try and solve this crisis," he said.
Talks with those who had fled the violence had redoubled his "determination that now, with a newly elected American president, we have got to do more to help this part of the world, to help Syria achieve transition," Cameron added.
He flew to the camp by helicopter with Jordanian Foreign Minister Nasser Judeh and announced that Britain would offer an extra 14 million pounds ($22 million) in humanitarian aid, bringing its total funding to 53.5 million pounds ($85.5 million) - making it the second largest donor after the United States.
Cameron later held talks with Jordan's King Abdullah II in the capital, Amman.
(Copyright 2012 by The Associated Press. All Rights Reserved.)