Iran will give a decisive response to any mistake by the United States in the Gulf and has stepped up patrols to secure passage of national flagged shipping, the Revolutionary Guards navy said overnight Sunday.
It was the first time Iran has acknowledged that it had an encounter with US warships in the Arabian Gulf last week, but alleged, without offering evidence, that American forces were responsible.
The incident on Wednesday prompted the US Navy to release video of small, high-speed Iranian boats closing on American warships during helicopter operations in the northern Gulf near Kuwait.
In the IRGC's telling, its forces were on a drill and faced "the unprofessional and provocative actions of the United States and their indifference to warnings". It said the Americans later withdrew.
The IRGC provided no evidence of any kind to support its allegation. It also accused US forces of blocking Iranian warships on April 6 and April 7.
"We advise the Americans to follow international regulations and maritime protocols in the Gulf and to refrain from any adventurism and false and fake stories," Sunday's statement from the IRGC said.
"They should be assured that the Revolutionary Guards navy and the powerful armed forces of the Islamic Republic of Iran see the dangerous actions of foreigners in the region as a threat to national security and its red line and any error in calculation on their part will receive a decisive response."
Lt Pete Pagano, a spokesman for the US Navy's Bahrain-based 5th Fleet, said the service stood by its description of the incident.
"Regarding any other interactions with our ships, US forces continue to remain vigilant and are trained to act in a professional manner," Lt Pagano said.
On the Iranian force's Sepah News website, the IRGC's navy said that any "mistake" by the US in the Gulf would meet with a decisive response.
The US military said that on Wednesday 11 vessels from the IRGC had sailed close to US Navy and coastguard vessels in the Gulf, calling the moves "dangerous and provocative".
At one point, the Iranian vessels came within 10 yards of the US Coast Guard cutter Maui, the US military said.
While such incidents occurred occasionally a few years ago, they had stopped. But tensions between the two states spiked this year after the United States killed Qassem Suleimani, the head of Iran's elite Quds Force, in a drone strike in Iraq.
The incident came amid heightened tensions between Iran and the US. Armed men boarded a Hong Kong-flagged tanker ship on Tuesday off the coast of Iran near the crucial Strait of Hormuz, holding the ship for a short time before releasing it.
Although Iran has not acknowledged the incident, private security firms said the IRGC was behind the seizure.
In a tweet on Sunday, Iranian Foreign Minister Mohammad Javad Zarif kept up his criticism of President Donald Trump, claiming Iran soon would export ventilators despite facing one of the world's worst coronavirus outbreaks.
"All you need to do is stop interfering in the affairs of other nations; mine especially," Mr Zarif wrote. "And believe me, we do not take advice from ANY American politician."
The US has refused calls to ease strict sanctions on Iran but has offered aid – a move rejected categorically by Tehran.
President Donald Trump again said Sunday he would be willing to provide aid to Iran to help deal with the coronavirus pandemic if Tehran requested it.
"If Iran needed aid on this, I would be willing," Mr Trump said at a White House briefing.
