British Prime Minister David Cameron on Thursday defended the policy of not paying ransom to terrorist groups for the release of kidnapped civilians.

“I know it is difficult to hear and I have thought about this very carefully. I am absolutely convinced that the policy of not paying ransoms to terrorists for kidnaps is right,” the British premier said ahead of the NATO Summit in Wales.

“I am in no doubt that those countries that have allowed ransoms to be paid that has ended up with terrorist groups including [the Islamic State] group having tens of millions of dollars that they can spend on kidnapping other hostages or preparing terrorist plots including against us here in the UK and in buying arms and weapons to wreak havoc,” he added.

“Since becoming prime minister I have ordered a number of hostage rescues in different parts of the world,” said Cameron, but reiterated, “We shouldn’t pay ransoms to terrorists. We shouldn’t let terrorists change our policy or our approach to this appalling problem of ISIS in Iraq and Syria.

“We need to show real resolve and determination. We need to use every power and everything we have in our armory with our allies, with those on the ground, to make sure we absolutely do all we can to squeeze this dreadful organization out of existence,” he concluded.

Earlier Thursday, Cameron and U.S. President Barack announced they intend to build an international coalition against the Islamic State (IS), the terror group that has conquered large portions of Iraq and Syria.

In the wake of the revelation of a second video showing the beheading of a Western journalist by IS this week, Obama and Cameron said they intend to lobby for the coalition’s assembly at the NATO summit.