US President Barack Obama has stressed the need to implement a draft deal for the cessation of hostilities in Syria and warned Russia and its allies that the "world will be watching."
Obama me with his top national security advisors just hours before the deal is due to take effect to plan ahead and discuss the campaign against the DAESH terrorist group.
"A lot of that is going to depend on whether the Syrian regime, Russia, and their allies live up to their commitments," he said in comments at the State Department.
"The coming days will be critical, and the world will be watching."
Obama cited the importance of the humanitarian aid, stressing all parties which are part of the deal need to end attacks including bombardment.
"Humanitarian aid must be allowed to reach areas under siege," he said.
Many in the Obama administration and some independent observers expressed doubts over whether a partial cessation deal would hold.
"None of us are under any illusions. We're all aware of the many potential pitfalls, and there are plenty of reasons for skepticism, but history would judge us harshly if we did not do our part in at least trying to end this terrible conflict with diplomacy," Obama said.
Obama also reiterated his view that Assad must step down or be removed from power if a lasting peace is to be found.
"It's clear that after years of his barbaric war against his own people - including torture, and barrel bombs, and sieges, and starvation - many Syrians will never stop fighting until Assad is out of power," Obama said.
"There's no alternative to a managed transition away from Assad."