NATO cannot run on the impulses of the US president, EU foreign policy chief Josep Borrell said on Monday in Brussels.
Responding to comments from former US president Donal Trump, Borrell said that the military alliance "cannot be à la carte."
On the campaign trail in the state of South Carolina, the Republican frontrunner for the 2024 US presidential election said that he would "not protect" countries from Russia that did not reach NATO's defence spending requirements.
"In fact, I would encourage them to do whatever the hell they want," Trump said, referring to Russia, calling the alliance's collective defence commitments into question.
"During this campaign, we will see and listen to many things," Borrell said, dismissing Trump's comments, adding that he won't be commenting on any "silly idea" that comes out of the US presidential campaign.
Trump's campaign intervention comes as the US Senate is deciding on a $95.3-billion foreign aid bill for Ukraine and Israel, which the former president staunchly opposes.
The former US president has been pushing for higher contributions by the US's European counterparts in intergovernmental organisations such as NATO, and in aid for Ukraine.
"It is unclear to what extent the US will be able to maintain its military and civilian capabilities in the future," German State Secretary for Development Jochen Flasbarth added on Monday while talking about ongoing political tussle in the US over Ukraine aid.
"This means that Europe itself will face additional challenges, additional demands and additional responsibility," he added.
