British Prime Minister David Cameron said on Thursday it was increasingly likely a bomb brought down a Russian airliner over Egypt with the loss of 224 lives, and U.S. President Barack Obama said Washington was taking that possibility "very seriously".

But Moscow, which launched air strikes against Islamist fighters including Islamic State in Syria more than a month ago, said it was premature to reach conclusions that the flight was attacked.

In a telephone call, Russian President Vladimir Putin told Cameron it was important that assessments of the cause of the crash last Saturday be based on information from the official investigation, Interfax news agency reported.

Egypt, which depends on tourism as a crucial source of revenue, said there was no evidence a bomb was to blame.

A Sinai-based group affiliated with Islamic State, the militant group that has seized swathes of Iraq and Syria, has claimed responsibility for the crash, which if confirmed would make it the first attack on civil aviation by the world's most violent jihadist organization.

Cameron, who hosted Egyptian President Abdul Fattah al-Sisi on Thursday for a previously scheduled visit, said: "We cannot be certain that the Russian airliner was brought down by a terrorist bomb, but it looks increasingly likely that was the case."