Iran's Revolutionary Guards chief on Thursday warned the US of a "decisive response" after President Donald Trump said he instructed the US Navy to "shoot down" Iranian boats that harass American ships in the Gulf.

"We declare to the Americans that we are absolutely determined and serious... and that all action will be met with a decisive response that will be efficient and quick," Major General Hossein Salami told state television.

"We have also ordered our naval units to target (US boats and forces) if they try to endanger the safety of our ships or boats of war."

Tensions between decades-old foes the United States and Iran escalated again last week with Washington accusing its arch enemy of harassing its ships in the Gulf.

Trump took to Twitter on Wednesday after Iran's Revolutionary Guards said they had launched the Islamic republic's first military satellite.

The United States has accused Iranian vessels of harassing its ships in the Gulf
The United States has accused Iranian vessels of harassing its ships in the Gulf Navy Office of Information / Handout

The US president said he had "instructed the United States Navy to shoot down and destroy any and all Iranian gunboats if they harass our ships at sea".

Salami said last week's maritime incident was the result of "unprofessional and dangerous behaviour by the Americans in the Persian Gulf".

The Guards commander also indicated that US actions in the sensitive waterway had been hampered by an outbreak of the novel coronavirus.

"In last week's incident, there was operational turmoil and disorder among US naval units at sea," said Salami.

This, he added, was an indication that the "command and control of their military units may have been weakened by... the coronavirus disease."

Iran and the United States are among the countries hardest hit by the coronavirus pandemic.

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