In Geneva, US Secretary of State John Kerry today said that "several proposals" were being discussed aimed at finding a way to restore at least a partial truce in the war-torn country.
The latest partial truce in Syria does not cover Aleppo, the country's largest city and the scene of its worst violence in recent weeks.
Aleppo remains on knife's edge as rebels and government forces trade rockets and bombs across the northern city and its outskirts, according to activist monitoring groups.
Separately, a car bomb detonated in the rebel-held Salhin neighborhood of Aleppo, appearing to target an Islamic judiciary council. The explosion wounded a lawyer and several other people, according to the Local Coordination Committees, an activist network.
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The Syrian Civil Defense, also known as the White Helmets, which organizes rescue operations in opposition-held areas of Aleppo, said several civilians were killed and wounded, including a judge for the hard-line jihadist faction Ahrar al-Sham.
The government declared its cease-fire on Friday around Damascus, the capital's eastern Ghouta suburbs, and the coastal Latakia region, in the wake of two weeks of rising violence that spoiled a previous cease-fire brokered by the US and Russia in late February.
Russia's Tass news agency quoted Russian Lt Gen Sergei Kuralenko, head of the Russian coordination center in Syria, as saying that the Damascus area cease-fire was brokered by the Russia and the United States, "in agreement with the Syrian leadership and the moderate opposition.