Iran leader says Trump presidency sign of US 'decline'

Iran's supreme leader Ayatollah Ali Khamenei said Tuesday that Donald Trump's presidency shows the United States is in "decline", as the Islamic republic marked 30th death anniversary of its founder.

"The fate of more than 300 million humans is in the hands of a person with such characteristics, this is a sign of America's political decline," Khamenei said in a speech broadcast live on state television.

"In America itself there is so much discussion on his mental and moral stability," he said, attending a ceremony at the mausoleum of Ayatollah Ruhollah Khomeini.

"When such a person is the president of a country, this shows the political and moral decline of that country."

Iran and US leaders have ratcheted up the barbs and insults ever since Trump was elected as president in 2016.

Living up to his campaign promises, Trump withdrew the US in May 2018 from the landmark 2015 nuclear deal between Iran and major world powers and reimposed sanctions.

The war of words intensified after Iran's revolutionary guards were designated a "terrorist organisation", with Tehran hitting back by declaring the US a "state sponsor of terrorism" and Washington's forces in the region "terrorist groups".

Fears that the war of words could flare into a military clash escalated when Washington dispatched the USS Abraham Lincoln carrier group, an amphibious assault ship, a Patriot missile battery and B-52 bombers to the region.

Iran has rolled back some of its commitments under the nuclear deal and has threatened to turn its back on more of the accord if it does not receive sanctions relief.