Turkish Prime Minister Recep Tayyip Erdogan has said the international community would have to accept the right of Syrians to self defence if the United Nations Security Council cannot solve the conflict there.
Mr Erdogan was speaking at the "Friends of Syria" conference in Istanbul where representatives of more than 70 countries are meeting to discuss the Syrian uprising.
The Arab League's Nabil al-Arabi called on participants of the conference to "simultaneously call on the Security Council to take a binding decision ... to stop the violence in Syria."
"If United Nations Security Council refrains from taking on the responsibility, the international community will have no chance but to accept Syrians' right to self-defence," Mr Erdogan said as he opened the conference.
And US Secretary of State Hillary Clinton said that by launching new assaults just days after accepting a peace plan by UN-Arab League envoy Kofi Annan, President Bashar al-Assad's regime was adding to a long list of broken promises.
"Nearly a week has gone by, and we have to conclude that the regime is adding to its long list of broken promises," Mrs Clinton said, according to prepared remarks distributed by the US State Department.
Ahead of the gathering, President Assad's regime declared victory over rebels and again voiced support for Mr Annan's plan, but kept up its shelling of rebel positions and said it had no plans to immediately withdraw troops.
And as the Istanbul gathering began, violence in Syria killed at least 16 people today, including eight soldiers who died during ambushes and gun battles in the east, northwest and near Damascus, monitors said.
Reports from Syria cannot be independently verified as state authorities have barred international journalists and rights groups.
The opposition Syrian National Council, meanwhile, called on the international community to recognise the group as the sole representative of the Syrian people.
"We want the recognition of the SNC as the sole legitimate representative of the Syrian people," Council head Burhan Ghalioun told reporters in Istanbul.
French Foreign Minister Alain Juppe said the conference would recognise the SNC as the main interlocutor, and had agreed to create a working group to consider further sanctions against Damascus when it meets in Paris within the next two weeks.
The SNC also announced that it would pay for the salaries of all those fighting Mr Assad's regime.
The meeting in Istanbul aims to find new ways to pressure the Assad regime into accepting the Annan plan to stop its crackdown on an Arab Spring-inspired uprising that the UN says has killed more than 9,000 people in the past year.