WARSAW, Poland: The head of the NATO military alliance warned Sunday that Donald Trump was putting the safety of US troops and their allies at risk after the Republican presidential front-runner said Russia should be able to do 'whatever the hell they want' to NATO members who don't meet their defense spending targets.

'Any suggestion that allies will not defend each other undermines all of our security, including that of the U.S., and puts American and European soldiers at increased risk,' NATO Secretary-General Jens Stoltenberg said in a statement.