Iran’s Revolutionary Guard Corps (IRGC) navy warned vessels to stay away from US warships in the Strait of Hormuz after overnight skirmishes, saying that sometimes it needs to teach “Yankees” a lesson, according to an audio recording shared with CNN.

“We advise you to keep a distance of at least 10 miles from the warships for your safety, because sometimes we need to teach Yankees (a) lesson” with “missiles and drones,” a voice was heard saying on VHF Channel 16, the radio frequency used by international ships for urgent communications.

A maritime industry source told CNN that on Thursday “the Iranians called on all the ships which were in the northern part of the Strait to move down closer to Dubai, which they all did,” adding that there was “intense gunfire” in the waterway that day.

Traffic in the Strait of Hormuz “remains significantly reduced,” the United Kingdom Maritime Trade Operations Centre (UKMTO) reported, with several new security-related incidents reported “in the last 48 hours.”

Operating in the waterway “remains high risk based upon recent attacks on ships in the area,” UKMTO said, adding that “blockade-related enforcement activity continues.”

Another source operating in the Iranian maritime industry told CNN that the chances of a “successful amicable resolution to this conflict” remains minimal. “We have some concern that the war may commence soon,” the source said.

Since the US and Israel began airstrikes against Iran at the end of February, Iran has threatened to strike any ship passing through the Strait of Hormuz without permission from the IRGC navy.