Britain's cyberspying chief has warned that artificial intelligence is becoming an “unstoppable force” weaponized just below traditional warfare levels.

The head of the U.K.'s National Cyber Security Centre warns that hostile nations like Russia, Iran and China are behind the most serious cyberattacks in the U.K. In a speech Wednesday, Richard Horne said British businesses need to prepare for large-scale cyberattacks, especially if the U.K. becomes involved in international conflicts.

British retailer Marks & Spencer says it's “working day and night” to resolve a cyberattack nearly two weeks ago that has left it unable to process any online orders.