London: Prime Minister David Cameron on Wednesday condemned the "barbaric" attack on the office of French satirical weekly Charlie Hebdo, saying Britain stood with its ally against "all forms of terrorism".

Cameron made the comments about the attack in Paris, in which 12 people were killed, at the start of his weekly question and answer session in parliament's lower House of Commons.

"I'm sure the whole House will want join me in condemning the barbaric attack this morning on an office of a magazine in Paris," he said.

"While details are still unclear, I know that this house and this country stands united with the French people in our opposition to all forms of terrorism and we stand squarely for free speech and democracy.

Earlier, Cameron said in a Twitter message that the killings were "sickening", while Foreign Secretary Philip Hammond said he was "appalled" to hear about the "apparent terrorist attack".