Prime Minister Cameron warns that ISIS is preparing to attack Britain.

Reuters reported on June 29 that British Prime Minister David Cameron warned that the self-proclaimed Islamic State (IS) in Syria and Iraq was planning attacks against Britain and posed an existential threat to the West.

British Prime Minister David Cameron. (Photo: CNN).

Speaking on the BBC, Cameron stated: "There are those in Iraq and Syria plotting to carry out horrific acts in Britain and elsewhere, and as long as ISIS exists in those two countries, we are under threat."

In an article in the Daily Telegraph, Cameron also expressed his desire for the British government to take a tougher stance against Islamic extremists in the country.

Earlier, Islamist gunmen killed up to 30 British tourists in an attack on June 26 in Tunisia, which British politicians described as the worst attack on British citizens since the London Underground bombings in 2005.

Currently, the international terrorist threat level in the UK is set at "severe" – the second highest level – meaning the likelihood of an attack is "very high."

Police said they have launched one of the largest counter-terrorism operations in a decade following the massacre in Tunisia.