British Prime Minister David Cameron wants lawmakers to consider the option of Britain joining U.S.-led air strikes against Islamic State of Iraq and Syria (ISIS) militants in Syria, his spokeswoman said on Thursday.

The British government believes a deadly Islamist attack in Tunisia last week, in which 30 Britons were killed, has underlined the threat the militant group poses and that London must think about doing more against ISIS as a result.

"What has changed is the growing evidence that ISIL (ISIS) poses a threat to people here in Britain and our national security," Cameron's spokeswoman told reporters.

"And in that context the prime minister does think that MPs (lawmakers) should be thinking about these issues and about what we are doing to tackle ISIL."

Cameron would not ask parliament to vote on the issue imminently, she signaled, saying the question would need to be considered "properly and carefully deliberated" beforehand.

But he believed there was a legal case to take such action, she said, saying Britain was already flying drones and planes over Syria to gather intelligence that could be used in any future strikes.

REUTERS