Prime Minister David Cameron is poised to agree to a role for Syrian President Bashar al-Assad during a transition period as part of a renewed diplomatic drive to end the Syrian conflict. In his speech at the UN, the British premier would, however, insist that Assad would eventually leave.

In a bid to "inject momentum" to solve the Syrian crisis, Cameron will back the views earlier expressed by Foreign Secretary Philip Hammond at the Commons foreign affairs committee.

"The prime minister's view is that there is not a long-term, stable, peaceful future for Syria where Syrian people can return home with President Assad as its leader, and that's what we've got to work towards ... We would be open to working with other countries on a solution whereby there is a transition. We haven't got a specific timeframe for when we think Assad should go. We've always been clear that there would need to be some sort of transition," said a British government source, according to the Guardian.

US Secretary of State John Kerry has previously said he is hopeful of coming up with a political solution to the four-year-long crisis. The uprising-turned-civil-war has claimed more than 200,000 lives and displaced 11 million people, many of them landing up on European shores.

Cameron will make his remarks amid the ongoing military build-up by Russia in the region. Russian President Vladimir Putin has long argued that supporting Assad would help defeat Islamic State (Isis) militants in the region.

"We are clear ISIL [another acronym for IS] poses a threat as much to Russia as it does to Europe and other countries around the world and therefore we should be able to find a way forward to work together," a spokesperson for the British prime minister was quoted as saying by Sky News.

"ISIL and Assad are both the enemies of the Syrian people. We are still of the view that we need to tackle the threat from ISIL but we also need to find a political solution that leads to a transition away from President Assad to a different leader that can unite the people of Syria and an inclusive government that the international community can engage with to tackle the threat ISIL."