The United States and Russia have announced a ceasefire in war-torn Syria will come into effect on February 27.

The second ceasefire plan in as many weeks calls on the warring parties to stop fighting by the end of the week, but specifically excludes the Islamic State group and the Al Qaeda franchise Al Nusra Front.

Those groups will still be targeted.

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“If implemented and adhered to, this cessation will not only lead to a decline in violence, but also continue to expand the delivery of urgently needed humanitarian supplies to besieged areas and support a political transition to a government that is responsive to the desires of the Syrian people,” US Secretary of State John Kerry said in a statement.

US President Barack Obama called Russia’s Vladimir Putin to discuss their joint efforts to bring about the ceasefire, the White House said, cautioning that the road ahead would not be easy.

“This is a moment of opportunity and we are hopeful that all the parties will capitalise on it,” White House spokesman Josh Earnest told reporters as he revealed the call between the two leaders.

“This is going to be difficult to implement.”

The US backs the rebels while Russia backs the Syrian Government in the conflict.

As the deal was taking shape, the UN inquiry on Syria released a report criticising international powers for feeding military escalation while talking peace.

– ABC, with wires