The US is expected to offer to cooperate with Russia in Syria, in a controversial pact which would see Washington effectively change course and help shore up President Bashar al-Assad.

John Kerry, the US secretary of state, arrived in Moscow for two days of meetings with Vladimir Putin and Sergei Lavrov, the Russian foreign minister, including on US proposals for a military alliance aimed at defeating extremist groups in Syria.

The former Cold War foes support opposing sides in the conflict, with Russia bombing in support of the Syrian government, and the US arming and training rebels.

The deal would see them working together to attack Islamic State of Iraq and the Levant (Isil), but also al-Qaeda-aligned Jabhat al-Nusra jihadists, who have been locked in fierce battles with the regime.

Nusra has been a thorn in Assad’s side but has so far not been the focus of the US-led coalition’s campaign, which has concentrated on routing Isil.

The Obama administration is suggesting a new command-and-control headquarters near Amman in Jordan that would house US and Russian military officers.

The "Joint Implementation Group" would "enable extended coordination" between their militaries on the Syrian battlefields.

Both countries would have to agree on targets before either one launches aerial attacks.