WASHINGTON: The United States will destroy any Iranian drones that fly "too close" to its ships in the Strait of Hormuz and has evidence that it shot down a drone on Thursday, a senior Trump administration official said on Friday.

Iran dismissed US President Donald Trump's assertion that the US Navy destroyed one of its drones. Iran said all of its unmanned planes were accounted for, amid growing international concern that both sides could blunder into a war in the Gulf.

"If they fly too close to our ships, they'll continue to be shot down," the Trump administration official said, briefing reporters on condition of anonymity.

The official said "we have very clear evidence" that US Navy warship Boxer shot down an Iranian drone. "We're confident," the official said.

A video of the incident could be released by the Pentagon, the official said.

The official also dismissed an offer made by Iranian Foreign Minister Mohammad Javad Zarif that Iran could immediately ratify a document prescribing more intrusive inspections of its nuclear program if the United States abandoned its economic sanctions on Tehran.

Relations between the United States and Iran have worsened since last year when Trump abandoned a 2015 international nuclear deal between world powers and Iran. Under the pact, Iran agreed to restrict nuclear work long seen by the West as a cover for developing atomic bombs in return for lifting sanctions.

Zarif appeared to have no decision-making ability and that Washington "would not consider anything from him serious," the official said.

Asked whom the United States would need to hear from in order to have negotiations over Tehran's nuclear program, the official said: "I would say the supreme leader or the president."

Trump remained open to negotiations with Iran without preconditions on its nuclear program and will maintain a tough economic sanctions regime on Tehran in the meantime, the official said.