"Iran is in serious financial trouble. They want desperately to talk to the U.S., but are given mixed signals from all of those purporting to represent us, including President Macron of France," Trump tweeted.

Trump has imposed crippling sanctions on Iran and sought to sink an international deal for managing the country's contested nuclear industry, but several major allies and other partners, including France, have resisted the US attempt to isolate the Iranians.

That division over how to handle Iran appears to be frustrating Trump, who is now left with few options other than to keep adding US pressure on Tehran -- so far with little tangible benefit.

Trump lashed out at Macron, saying "I know Emmanuel means well, as do all others, but nobody speaks for the United States but the United States itself. No one is authorized in any way, shape, or form, to represent us!"

As the US-Iranian standoff deepens, tensions are soaring in the strategic region, with drones downed, tankers seized by Tehran and mysterious attacks on ships in Gulf waters.

Washington and its Gulf allies have accused the Islamic republic of the attacks on ships, which Tehran denies.

In response, the US has been seeking to form a coalition whose mission-- dubbed Operation Sentinel -- it says is to guarantee freedom of navigation in the Gulf.

Britain, which already has warships on protection duty in the Gulf after a UK-flagged tanker was seized by Iranian Revolutionary Guards, has said it will join the planned operation.

But other European countries have kept out, for fear it might harm European efforts to reach a negotiated settlement with Iran.