Western and Arab nations warned President Bashar al-Assad not to delay adopting a plan to end a year of bloodshed in Syria and called on peace envoy Kofi Annan to set a timetable for action if the violence continues.
Annan is due to brief the U.N. Security Council on Monday about whether he has seen any progress towards implementing his proposals, which Damascus has accepted but not yet carried out.
After their meeting in Istanbul on Sunday, the Friends of Syria said Assad did not have an open-ended opportunity to meet his commitments to Annan, who is seeking a ceasefire, troop withdrawals from cities and access for humanitarian aid.
The group made no mention of arming the rebel Free Syrian Army (FSA), as advocated by some Gulf Arab states, but said it would continue to work on additional appropriate measures with a view to the protection of the Syrian people.
Hardline Gulf states are likely to interpret the phrase as a licence to fund, if not arm, the FSA, while the United States and others will see it as allowing supplies of non-lethal equipment to the loosely organised armed opposition to Assad.
U.S. Secretary of State Hillary Clinton said her government was supplying communications equipment that will help activists organise, evade attacks by the regime and connect to the outside world and was discussing with other nations how best to expand this support.
Ministers from the United States, Europe and Arab countries attended the Istanbul meeting but Security Council members China and Russia and Syria's ally Iran were prominent absentees, reflecting the divided international response to Syria's crisis.
The regime will be judged by its deeds rather than its promises, said a communiqué issued by representatives of 83 nations in Turkey. It called on Annan to determine a timeline for next steps, including a return to the U.N. Security Council, if the killing continues.
Violence has raged unabated despite Annan's mediation.
The Syrian Observatory for Human Rights reported 70 people were killed across Syria on Sunday, including 12 civilians killed in bombardment and sniper fire in the city of Homs. Nineteen soldiers and 12 rebel gunmen were killed in clashes.
We will not let the Syrian regime misuse another opportunity, which is the last chance for the situation in Syria, Turkish Foreign Minister Ahmet Davutoglu told a news conference after the meeting he hosted.
The Friends of Syria recognised the opposition Syrian National Council (SNC) as a legitimate representative of all Syrians, and noted it as the main opposition interlocutor with the international community - wording that fell short of full recognition of a group hampered by chronic disunity.
Clinton berated Assad for not acting on Annan's peace plan. Nearly a week has gone by, and we have to conclude that the regime is adding to its long list of broken promises, she said.
There is no more time for excuses or delays ... This is a moment of truth, Clinton told a news conference later.
Western powers have been wary of military intervention in Syria, but Davutoglu sounded an alarm bell, comparing the situation there to the plight of Bosnia in the 1990s.
In the case of Bosnia, the international community was too slow ... therefore we lost many people, he said. In the case of Syria ... we have to act without delay.
Chris Phillips, a Middle East expert at the University of London, said the Istanbul meeting had produced little.
It's another damp squib from the international community, reflecting the fact that their hands are tied, he said, citing divisions over arming the rebels between the West and Arab League hawks such as Qatar and Saudi Arabia.
They have a very limited amount of leverage that they can place on the Assad regime, Phillips said, noting that the group's endorsement of Annan's plan had effectively dropped previous Arab and Western demands for Assad's removal.
Annan will brief the U.N. Security Council at 1400 GMT on Monday on his efforts to calm a conflict in which Syrian security forces have killed more than 9,000 people, by a U.N. estimate, while rebels have killed 3,000 troops and police, according to Damascus.
The rebel FSA said on Saturday it would stop shooting if Assad pulled heavy weaponry out of urban areas, but Damascus said its forces must stay to maintain security.
If Annan's plan falters, the next steps could include a return to the Security Council for a binding resolution, with increased pressure on Assad's allies Russia and China, which have endorsed Annan's mission, to get tough with Damascus.
If the former U.N. chief signals progress, Council diplomats say work could start on a resolution to send 200 to 250 unarmed U.N. observers to Syria to monitor an eventual ceasefire.
(Editing by Alison Williams)