London - British 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".Terrorist attackBlack-hooded gunmen shot dead at least 12 people at the Paris offices of the satirical newspaper on Wednesday, a publication firebombed in the past after publishing cartoons lampooning Muslim leaders and the Prophet Muhammad, Reuters reported.President Francois Hollande headed to the scene of the attack after government confirmed it was raising France's security level to the highest notch."This is a terrorist attack, there is no doubt about it," Hollande told reporters.Another 10 people were injured in the incident and police union official Rocco Contento described the scene inside the offices as "carnage"."About a half an hour ago two black-hooded men entered the building with Kalashnikovs (rifles)," witness Benoit Bringer told the TV station. "A few minutes later we heard lots of shots," he said, adding that the men were then seen fleeing the building.France is already on high alert after calls last year from Islamist militants to attack its citizens and interests in reprisal for French military strikes on Islamist strongholds in the Middle East and Africa.