Summary John Kerry warned there was "a lot more work to do" for a ceasefire in Syria.
LONDON (AFP) - US Secretary of State John Kerry warned there was "a lot more work to do" for a ceasefire in Syria that had been due to begin on Friday, as Kurdish-led forces seized a key town from the Islamic State group.
"Everyone recognises the complexity of this endeavour, and there is certainly a lot more work to do," Kerry said in a statement during a visit to London.
Kerry said talks between US and Russian negotiators had been "serious and so far constructive, with a few tough issues still to resolve".
"We want this process to be sustainable, and should all participants prove willing to really sit down and work this out, we can get to a cessation of hostilities," Kerry said.
"Coupled with the delivery this week of desperately needed humanitarian aid -- food, water and medicine -- we have a chance right now to really make a difference on the ground," he added.
The truce has failed to materialise so far, with the UN s Syria envoy also acknowledging that a proposed February 25 date to restart stalled peace talks was no longer "realistically" possible.
Meanwhile, tensions between regime backer Moscow and opposition supporter Ankara escalated, with Russia convening a UN Security Council meeting for later Friday to discuss the possibility of a Turkish ground intervention in Syria.
On the ground, the Kurdish-led Syrian Democratic Forces alliance seized the town of Al-Shadadi from IS, with backing from US-led air strikes, a monitor and Kurdish sources said.
