London, July 19 (IANS): British Prime Minister David Cameron has said his country is committed to working with the US to destroy the "caliphate" set up by the Islamic State (IS) terror group in Iraq and Syria, a media report said on Sunday.

"I want Britain to do more," the prime minister said on Saturday.

"We're talking and discussing at the moment, with the opposition parties in Britain, about what more we can do. But be in no doubt, we're committed to working with you (US) to destroy the caliphate in both countries," BBC quoted Cameron as saying.

Last week, the Labour party's interim leader Harriet Harman was invited to a National Security Council briefing on the threat in Syria. The development is being seen as a sign of a possible parliamentary vote to extend airstrikes in the autumn.

Labour and the Liberal Democrats have called for an explanation in parliament after it emerged that Royal Air Force pilots had already taken part in bombing raids over Syria despite MPs having approved action against IS only in Iraq.

Downing Street has confirmed that Cameron was aware of the Syria missions.

Cameron is expected to give a speech on Monday, to put in place the government's future strategy to combat radicalisation and extremism.