An open-ended ceasefire in southern Syria brokered by the United States and Russia has come into effect.

The ceasefire, announced after a meeting between US President Donald Trump and Russian President Vladimir Putin in Hamburg last week, is the first initiative by the Trump administration in collaboration with Russia to bring some stability to war-torn Syria.

No ceasefire has lasted long in the six-year-old Syrian war.

US-backed rebels, Syrian government forces and Islamic State militants are all fighting for control of southern Syria.

The latest truce is intended to allay concerns of neighbouring Israel and Jordan about Iranian-backed and government-allied forces at their borders. The truce does not include the IS group.