MUNICH (AFP) - Russia must change its military targeting as it backs the Syrian regime, US Secretary of State John Kerry said on Saturday (Feb 13), as world powers seek a cessation of hostilities in the war-torn country within a week.

"To date, the vast majority of Russia's attacks have been against legitimate opposition groups," Mr Kerry said. "To adhere to the agreement it made, we think it is critical that Russia's targeting change."

Russia has supported the regime of President Bashar al-Assad against rebel forces whom it collectively labels "terrorists". The United States has provided some support to the rebels and called for Mr Assad to leave power.

Friday's agreement called for a "cessation of hostilities" within a week and for greatly increased humanitarian access, but it excludes the Islamic State in Iraq and Syria (ISIS) group and al-Qaeda-linked extremists.

"There's a lot of work to do before an effective cessation can commence," Mr Kerry said.

He stressed this was the crucial moment in a five-year war that has claimed more than 250,000 lives.

"This is the moment. This is a hinge point," he said. "Decisions made in the coming days and weeks, and a few months could end the war in Syria - or could define a very difficult set of choices for the future."

He added: "The war in Syria has now lasted for almost five years - and shows no signs of burning itself out - which is why we are so focused on a political track."