The United States was set to boost its support for Syria's rebels at a meeting of the opposition's main foreign backers Saturday and could for the first time agree to supply non-lethal military gear.
But Washington is expected to stop short of agreeing to rebel demands for arms as the 11-nation core group of the "Friends of Syria" hold talks in Istanbul with key figures in the opposition battling President Bashar al-Assad.
After arriving in Istanbul, US Secretary of State John Kerry met first with the head of the main opposition Syrian National Coalition, Ahmed Moaz al-Khatib.
Top diplomats from the 11 countries -- including the United States, European nations and Arab countries -- then met and began a working dinner with the opposition.
Ahead of the talks, a senior US official said Kerry would discuss increasing assistance to "moderate opposition groups" including the Coalition and the rebel Supreme Military Council.
The official said the aid to rebel fighters could go "beyond military food rations and medical kits to include other types of non-lethal supplies," but said the details still needed to be worked out.
US media reports have suggested Washington is preparing to provide protective battlefield equipment to the rebels such as body armour, armoured vehicles and night-vision goggles, as well as communications gear.
But such supplies may hinge on the opposition showing it can be more inclusive, protect minorities and respect human rights.
Speaking to US lawmakers this week, Kerry said Saturday's talks would be an effort to "get everybody on the same page with respect to what post-Assad" Syria will look like.
"We also want to make certain that the people we're working with are committed to pluralism, diversity, to a democratic process," Kerry said. "There have to be a series of guarantees."
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A Western diplomatic source said the Friends of Syria would be looking for the opposition to "take a firm stand on extremism and chemical weapons" and commit to finding a political solution to Syria's crisis.
-- Opposition urges 'surgical strikes' --
Voicing frustration at the lack of a strong international response, the opposition urged foreign supporters to carry out "surgical strikes" on positions used by Assad's regime to fire missiles on civilians.
"It is the moral imperative of the international community... to take specific, precise and immediate action to protect Syrian civilians from the use of ballistic missiles and chemical weapons," the opposition Coalition said in a statement.
Yaser Tabbara, a spokesman for the opposition's interim prime minister Ghassan Hitto, said new pledges of aid would not be not enough.
"Assad is firing missiles against densely populated areas... without consequences. Throwing money at the problem won't solve it," he said.
The Friends of Syria group has struggled to come up with a united strategy to end the violence in Syria, despite fighting that has seen more than 70,000 killed and hundreds of thousands forced from their homes.
Washington has been gradually shifting its policy on providing assistance to the opposition, with Kerry announcing at the last Friends of Syria meeting in February that the US would start providing direct non-lethal aid to rebel fighters.
But many in the West have raised concerns about arming the rebels, fearing weapons could fall into the hands of radical Islamist groups like the Al-Nusra Front, which this month pledged allegiance to Al-Qaeda.
Britain and France have been pushing for a European Union arms embargo to be allowed to expire by the end of May, but Paris has appeared more wary about arms supplies since the Al-Qaeda pledge.
Supporters of arms supplies have said the rise of Islamist groups like Al-Nusra is only a stronger argument for providing weapons to more moderate voices in the Syrian opposition.