The White House agreed to send communications equipment to help Syrian rebels organize and evade Syria's military, Secretary of State Hillary Clinton said.
The satellite communications equipment "will help activists organize, evade attacks by the regime and connect to the outside world," Clinton said at a "Friends of Syria" conference of 83 countries and international organizations in Istanbul, Turkey.
The Syrian National Council, the main opposition alliance, said the US assistance will include night-vision goggles.
"We are discussing with our international partners how best to expand this support," Clinton told the group, which seeks to find a solution to the Syrian crisis outside the UN Security Council, after Russia and China vetoed a council resolution on Syria.
The Obama administration will also give $12 million in humanitarian assistance for international organizations aiding the Syrian opposition, bringing the US total to $25 million, the U.S. State Department said.
Arab nations, including Saudi Arabia, Qatar and the United Arab Emirates, pledged $100 million to pay opposition fighters, known as the Free Syrian Army, in the hope the money would encourage soldiers loyal to President Bashar Assad to defect, officials said.
"We would like to see a stronger Free Syrian Army," SNC Chairman Burhan Ghalioun, a Syrian political sociology professor at Paris' New Sorbonne University, told the world leaders and other officials at the Sunday conference. "All of these responsibilities should be borne by the international community."
"This is high noon for action," he said.
An official Syrian newspaper cited by the British newspaper The Daily Telegraph said Saudi Arabia was already plotting to "arm the terrorists, encourage the bloodbath and destroy infrastructure."
Saudi Arabia had no comment Sunday.
Syria announced last week it accepted a six-point peace plan being promoted by Annan, a former UN secretary-general acting on behalf of the United Nations and the Arab League.
But Assad then demanded the "armed terrorist groups" he claims are supported by an Arab-Western "conspiracy" disarm first.
Since then, the regime has begun new assaults in Idlib and Aleppo provinces, killing hundreds, including at least 35 rebels, soldiers and civilians Sunday, opposition groups said.
"Nearly a week has gone by, and we have to conclude that the regime is adding to its long list of broken promises," Clinton told the conference as pro-Assad protesters demonstrated outside.
"The world must judge Assad by what he does, not by what he says," she said. "And we cannot sit back and wait any longer."
The Annan peace plan, backed by the UN Security Council, proposes a cease-fire, possibly monitored by UN observers, followed by "Syrian-led" negotiations to settle the crisis, with free access for aid agencies and the media.
It does not call for Assad's resignation.
Annan, who did not attend the Istanbul conference, was to brief the Security Council's 15 members in New York Monday on whether he has seen any progress toward carrying out his proposals.
"What some countries are saying is, 'If the Annan process does not work, we are going to have to look at arming the opposition,'" British Foreign Secretary William Hague said in Istanbul, adding Britain would not be among the countries arming the opposition.
Turkish Prime Minister Recep Tayyip Erdogan, the host of Sunday's meeting, called on the Security Council to act, saying Damascus was using its ostensible embrace of Annan's initiative to buy time.
"If the Security Council hesitates, there will be no option left except to support the legitimate right of the Syrian people to defend themselves," he said.
"They are not alone," he said of the opposition. "They will never be alone."
The Istanbul conference called on Annan to "determine a timeline" for the next steps in Syria, "including a return to the UN Security Council, if the killing continues."