Western and Arab nations sought to exert more pressure on Syrian President Bashar al-Assad on Sunday, April 1 mistrusting his acceptance of a plan to end a year of bloodshed, but were not expected to arm rebels or fully recognize an opposition council, Reuters reported.

Opening a Friends of Syria conference in Istanbul, Turkish Prime Minister Tayyip Erdogan told foreign ministers and other officials from some 70 countries that the "legitimate demands of the Syrian people must be met, right here, right now".

In her prepared remarks, U.S. Secretary of State Hillary Clinton urged members of Assad's government to halt operations targeting civilians, or face "serious consequences".

She said the United States was providing communications gear among other aid to Syria's civilian opposition, and denounced Assad for failing to follow through on his agreement to a peace plan proposed by U.N.-Arab League special envoy Kofi Annan.

The United States and its Gulf Arab allies, suspecting Assad of playing for time, urged Annan on Saturday to set a timeline for "next steps" if there was no ceasefire.

Violence has raged unabated despite Annan's mediation. Opposition activists reported at least 16 people killed on Sunday, mostly in clashes in northwestern and eastern Syria.

Syrian media derided the Istanbul meeting, which the Baath newspaper described as "a regional and international scramble to find ways of killing more Syrians and destroying their society and country, to reach the broad goal of weakening Syria".

Around 50 Assad supporters protested outside the conference centre, waving Syria, Russian and Chinese flags and brandishing pictures of the Syrian leader. "Allah, Syria, Bashar, that's it" and "Down, down USA" they chanted, before police removed them.

Mahmoud Abdulatif, a Syrian lawyer who joined dozens in a similar protest outside a conference hotel used by delegates, accused Gulf Arab leaders and others of meddling in Syria.