The United States is unlikely to heed calls to arm Syrian rebels any time soon despite backing the new opposition coalition, wary of being entangled in a long, bloody conflict, analysts said.

The leader of the new body, Ahmed Moaz al-Khatib, has urged the world to arm the rebels with "specialized weapons" to "cut short the suffering of the Syrians" in the 20-month war which has killed some 37,000 people.

Frustrated by months of in-fighting among the opposition, Washington had pushed for the formation of the Syrian National Coalition which emerged on Sunday from marathon talks in Doha.

Secretary of State Hillary Clinton Wednesday welcomed the moves to make the opposition "a more effective, representative body" with "credibility with those inside Syria who are doing the fighting and demonstrating, the dying."

But while the US has recognized the body as "a legitimate representative" of the Syrian people, it stopped short of calling it a de-facto government-in-exile, and remains resolute in its refusal to arm the rebels.

More needs to be done especially on the organizational side, but as the opposition "demonstrates its effectiveness in advancing the cause of a unified, democratic, pluralistic Syria, we will be prepared to work with them to deliver assistance to the Syrian people," Clinton told a press conference in Australia.

The United States Wednesday unveiled another $30 million in humanitarian help for the Syrian people, bringing its total aid to almost $200 million. And it has been providing non-lethal aid, such as equipment to allow rebel groups to overcome the regime's jamming of communications networks.

But France, the first country to greet the body as the "sole" representative of the Syrian people, has said countries must now review the arms issue.

President Barack Obama first called for Syrian leader Bashar al-Assad to step aside in August 2011, and the United States has slapped sanctions on the regime and sought in vain to win similar UN moves -- thwarted by vetoes by Russia and China.

Obama's re-election and an end to the bitter presidential campaign season, could now give the US administration more room to review its Syria strategy.

"The US has been virtually missing in action on Syria so far, but their recent moves, including the push for the formation of the coalition, indicates that they might be ready to adopt a more proactive attitude," said pro-democracy Syrian activist, Ammar Abdulhamid, a fellow at the Foundation for the Defense of Democracies.

"The heavy lifting, though, including arming rebels and perhaps pushing for a de facto no-fly zone, might still be left to other countries at this stage," he told AFP, explaining that Obama "does not want to see the US embroiled in another regional conflict... so we should not expect too much at this stage."

US analysts said questions remained over the new coalition, highlighting that a Kurdish body had still not joined, and pointing to deep concern about weapons and cash falling into the hands of militant groups hostile to the West.

The opposition now needs to work on setting up a transitional government and some form of military council, they said.

"What the United States is looking for... is one military organization where all military aid can be channeled, that in turn can be relied upon to distribute the money among fighting groups inside the country, leaving out the jihadi groups," said Marina Ottaway, senior associate with the Carnegie Endowment for International Peace.

"This is a very admirable plan, I'm not sure that it can work," she told AFP, adding "the idea that somehow by centralizing the distribution of money the jihadi groups will be cut off, I don't think it's realistic."

Abdulhamid agreed that before the international community could start arming the rebels a priority was that a "mechanism for vetting groups and delivery channels need to be agreed."

Even calls for a no-fly zone in Syria, similar to the NATO-led one set up in Libya, would prove problematic, being costly to set up and patrol, and carrying a high risk of casualties.

One game-changer could be if the US gives a nod to its allies in the region to supply weapons, such as Stinger shoulder-launched missiles, to the rebels.

"I think it's very unlikely that the US will provide the Stingers itself. Would it give an order to countries that bought Stingers from the United States to pass them along? That we don't know, but I think that if there is a change in US policy it's likely to be in that direction," Ottaway said.

Salman Shaikh, director of the Brookings Doha Center, said international support was crucial for the survival of the new coalition.

They "will get significant amounts (of money), especially from the Gulf countries, and they will also get weapons from some countries," said Shaikh "but not (from) the US."