Foreign ministers from more than 70 Western and Arab countries are meeting in Istanbul to explore ways to step up pressure on the Syrian regime and bolster the opposition.
The second so-called Friends of Syria meeting follows opposition calls for rebel fighters to be armed.
The opposition says President Bashar al-Assad's backing of a UN-Arab League peace plan is a ploy to win time.
The Syrian government, meanwhile, has declared victory over rebel fighters.
Activists say at least 25 people died in violence on Saturday, with security forces continuing bombardments in the city of Homs and other areas.
The foreign ministers meeting in Istanbul, who include US Secretary of State Hillary Clinton, are expected to maintain diplomatic pressure on President Assad, largely by insisting that he abide by the peace plan proposed by UN-Arab League envoy Kofi Annan.
President Assad's nominal acceptance of the six-point plan has been treated with scepticism by Western and Arab governments.
There are also likely to be pledges of more financial help - both for victims of the conflict and to help the main opposition group, the Syrian National Council (SNC), become a more effective organisation, says the BBC's Jonathan Head in Istanbul.
However, beyond that the conference can offer little, he adds.
Ahead of the talks, the SNC for the first time called on neighbouring countries to allow supplies of weapons to reach the insurgent Free Syrian Army.
"We have called for the need to arm the Free Syrian Army so that it may defend the lives of the Syrian people. We hope the Friends of Syria will adopt our position," SNC head Burhan Ghalioun said.
Our correspondent says the same demand is also backed by some Arab states - but not by most of the countries attending the Friends of Syria conference.
They fear a flood of weapons could fuel a sectarian civil war.
Mrs Clinton held talks with Saudi officials in Riyadh on Saturday to discuss ways to maintain pressure on Damascus.
Saudi Foreign Minister Saud al-Faisal - at a joint news conference with Mrs Clinton - said arming the Syrian opposition was a "duty" because the opposition "cannot defend itself except with weapons".
Mr Ghalioun, speaking in Istanbul, said he believed Mr Assad's acceptance of the peace plan was another "lie and a manoeuvre" to gain time.
"We have no illusions over the possibility of the mission's success because Bashar Assad and the Syrian regime have no credibility to engage in a political process," he said.
"It will soon become obvious the regime won't even implement the first clause of the agreement."
The peace plan calls for troops to be withdrawn from residential areas as a gesture of good faith.
However, on Saturday the Syrian government said troops would stay until "peace and security" prevailed.
Syrian Foreign Ministry spokesman Jihad al-Makdissi earlier told Syrian TV that "the battle to topple the state is over".
"Our goal now is to ensure stability and create a perspective for reform and development in Syria while preventing others from sabotaging the path of reform," he said.
Government forces have engaged in a string of military offensives against strongholds of the lightly armed Free Syrian Army in cities across Syria.
The UK-based Syrian Observatory for Human Rights said government troops had killed at least 25 people on Saturday, in the southern province of Deraa, the north-western province of Idlib and the central region of Homs.
Another activist group, the Local Co-ordination Committees, said security forces had killed 36 people including nine in Idlib and eight in Homs.
The figures cannot be independently verified.
The UN believes at least 9,000 people have died in the year-long revolt against Mr Assad's rule.
The Syrian government has been trying to suppress an uprising inspired by events in Tunisia, Egypt and Libya. The UN says thousands have been killed in the crackdown, and that many more have been detained and displaced. The Syrian government says hundreds of security forces personnel have also died combating "armed terrorist gangs".