US President Barack Obama and British Prime Minister David Cameron upped pressure on Moscow during a joint press conference at the White House Monday.

US President Barack Obama and British Prime Minister David Cameron upped pressure on Moscow during a joint press conference at the White House Monday.

Obama said Russia had an "interest as well as an obligation" to help end the violence, saying he had delivered a similar message to Russian President Vladimir Putin, ahead of Secretary of State John Kerry's Moscow visit last week.

He stated that “a leader on the world stage, Russia has an interest, as well as an obligation, to try to resolve this issue in a way that can lead to the kind of outcome that we'd all like to see over the long term.”

For his part, Cameron considered that “Syria's history is being written in the blood of its people, and it is happening on our watch.”

“The world urgently needs to come together to bring the killing to an end,” he added.

Cameron, who just returned from a visit to Russia, said he believed Washington, London and Moscow had found "common ground" on the crisis.