WASHINGTON (AFP) - US President Donald Trump on Friday (June 9) insisted that the United States remained committed to Nato's mutual defense pledge, after failing to endorse it in a speech in Brussels last month.

Amid worries by Washington's European partners that the US leader had not fully bought into the Atlantic alliance, Trump told reporters: "I'm committing the United States to Article Five. Certainly we are there to protect."

"That's one of the reasons that I want people to make sure we have a very, very strong force, by paying the kinds of money necessary to have that force," Trump told a joint press conference with visiting Romanian President Klaus Iohannis.

The US president stunned Europe's leaders at a summit in Brussels on May 25 when he failed to publicly back the now 29-member bloc's founding mutual defense guarantee, and instead castigated the allies for failing to pay their way.

According to Politico, Trump's defense and security advisors included in his prepared speech a clear endorsement of the mutual defense pledge, but Trump himself struck it out just before speaking.

Doubts have remained since then despite US diplomats and military leaders themselves restating the pledge.