A former Dutch prime minister and staunch Ukraine supporter who took the Atlantic alliance's reins early this month, Rutte was in London for a meeting with British Prime Minister Keir Starmer and Ukrainian President Volodymyr Zelensky.

"I know that he understands completely and agrees with me that this fight in Ukraine is not only about Ukraine, it's also about the safety and the future security of the United States. He knows this," Rutte said of Trump after the meeting.

"So, really, stop worrying about a Trump presidency."

Some NATO members fear a reduced US commitment to European security and an end to military support for Ukraine if the aid-sceptic Republican wins the presidential election on November 5.

On the campaign trail, Trump has threatened not to protect NATO members who do not spend enough on defence and promised a quick deal with Russian President Vladimir Putin to end the war.

Rutte had already dismissed the fears surrounding a possible Trump win when he took over as NATO secretary general.

"I'm not worried. I know both candidates very well. I worked for four years with Donald Trump," Rutte said then, addressing concerns over the impact the US vote could have on the alliance.