The crisis in Syria is becoming "more complicated" by Russian involvement in tackling Islamic State, the Foreign Secretary has said after talks with his US counterpart.
Philip Hammond said the possibility of a fresh vote on British military action in Syria is kept under constant review but indicated the Government has reservations about any involvement by the Federation, a key ally of Bashar Assad's regime.
US Secretary of State John Kerry, who is on a three-day visit to the UK, said American and Russian defence secretaries had held extensive talks by telephone on defeating IS, also known as Isil.
Speaking after the meeting at the Foreign Secretary's official residence in London, he said: "Would we welcome Russian help in going against Isil? Obviously. We have talked about it for some period of time."
He added: "But the other part of the equation is Assad and how you resolve the fact that he is a magnate for foreign fighters to come to the region."
Mr Hammond said the Government had been clear that if it believed airstrikes in Syria were necessary it would go back to parliament.
He said: "We keep that situation under continuous review and we will continue to talk to our allies about the military situation in the round."
He added: "Because of the Russian engagement, the situation in Syria is becoming more complicated. I think we need to discuss this as part of a much bigger problem, the migration pressures, the humanitarian crisis in Syria as well as the need to defeat Isil."