DHAKA: The Islamic State in Iraq and Syria (ISIS) claimed the beheading of a British aid worker on Saturday, an act slammed as ‘pure evil’ by UK prime minister David Cameron who vowed Britain would do all it could to catch the killers.

President Barack Obama offered US support for its ‘ally in grief’, while Cameron faced growing calls to allow Britain’s military to help in Washington’s planned assault against the rampaging jihadist group.

The British premier will chair a meeting of the government’s emergency Cobra committee early Sunday in response to the online video purportedly showing a masked IS militant killing hostage David Haines in retribution for the US and British campaign against the group.

Cameron called the attack ‘a despicable and appalling murder of an innocent aid worker’ and ‘an act of pure evil’.

‘We will do everything in our power to hunt down these murderers and ensure they face justice, however long it takes,’ he said in a statement, reports The Straits Times.

BDST: 1228 HRS, SEP 14, 2014