David Cameron and Russian premier Vladimir Putin have agreed to "work together" to defeat the Isis militant group, the two leaders have said.
The commitment comes after a telephone conversation between the pair early on Wednesday, according to a Downing Street report of the diplomatic exchange.
Mr Cameron had asked Mr Putin to update him on Russian operations against militants in Syria in light of the start of British air strikes in the country.
Mr Putin also requested the assistance of British experts in analysing information on the flight recorder of a Russian jet shot down by Turkish forces during the course of the conflict.
Russian war planes are bombing militants opposed to the Assad regime in the country, including Isis, which is also known as Islamic State and Daesh.
The UK extended air strikes against Isis from Iraq to Syria after a parliamentary vote on the matter last week.
The Prime Minister is said to have told Mr Putin that the UK is still opposed to the Syrian president Bashar al-Assad remaining in charge in Syria.
Mr Assad is backed by Russia and his forces are also reportedly fighting against Isis to the south and west of the city of Homs, among other areas.
The phone call comes after Mayor of London Boris Johnson said the UK should work with Putin over Isis.
Mr Putin has met with US president Barack Obama in November where they agreed “a Syrian-led and Syrian-owned political transition” for the country.
A Downing Street spokesman said Mr Cameron offered his condolences to Mr Putin over the death of a Russian pilot, whose plane was shot down by Turkish missiles following an alleged air space infraction on Syria's border. Turkey is a member of the Nato alliance, which the UK is also a member of.
"They agreed that it was important to wait for the investigation to establish what had happened and the Prime Minister said he would consider president Putin's request to send British experts to assist the investigation," the spokesperson said in statement describing the conversation.
"The Prime Minister updated the president on the recent House of Commons vote and the strong mandate the UK Government now has to take part in air strikes in Syria, as well as Iraq, to target Daesh.
"The Prime Minister and president agreed that the UK and Russia should work together, with other international partners, to tackle Daesh and the threat it poses, and on the political process to bring peace to Syria.
"Agreeing that military action alone would not defeat Daesh, both leaders discussed the importance of a political process to deliver peace in Syria and the Prime Minister underlined the need for a government that all the Syrian people can support."
Around a dozen of Mr Cameron's Conservative MP defied their leader and either voted against or abstained on his whipped vote to extend air strikes in Syria.
They joined the bulk of Labour MPs and the opposition party's leader Jeremy Corbyn, who said the case for air strikes had not been proven.
A larger group of Labour MPs, number 66, ensured that the air strikes were supported by a significant majority in the House of Commons, however. Mr Corbyn allowed his MPs to vote according to their conscience.
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