Washington DC - President Donald Trump on Thursday promised $10 billion for a new "Board of Peace," an amorphous new institution focused first on Gaza, that is being launched just as he threatens Iran with war.

While US warplanes and aircraft carriers headed toward Iran on his orders, Trump welcomed some two dozen allies from around the world to the gleaming Washington building of the former US Institute of Peace, which has been gutted and renamed after the 79-year-old Republican.

Trump, who has sharply curtailed foreign aid, said that the US would contribute $10 billion to the initiative, whose goals include rebuilding Gaza, which was reduced to rubble by two years of war between Hamas and Israel.

"Together we can achieve the dream of bringing lasting harmony to a region tortured by centuries of war, suffering," said the realtor-turned-president, who has previously spoken improbably of building tourist resorts in Gaza.

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Trump did not explain exactly where the money would go, and his "Board of Peace" has drawn wide criticism for its opaque nature.

Trump will wield veto power over the "Board of Peace" and can remain its head even after leaving office, while countries that want to stay on permanently rather than enjoy a two-year stint will need to pay $1 billion.

In a rambling speech in which he denounced domestic opponents, highlighted stock market gains, and hailed his prowess in endorsing foreign leaders during elections, Trump said he wanted to pursue more peace deals.

"It's all about an easy word to say, but a hard word to produce – peace," Trump said.