Dubai. Iran's Revolutionary Guard navy on Saturday warned that any attack on Iranian oil tankers or commercial vessels would be met with a “heavy assault” on one of the US bases in the region and enemy ships, even as a tenuous ceasefire appeared to be holding.

Iranian state TV reported the warning a day after the United States struck two Iranian oil tankers, casting doubt on the month-old ceasefire that the US has insisted is still in effect. The US military said the tankers were trying to breach its blockade of Iran’s ports.

Meanwhile Britain’s defense ministry said it was deploying a warship to the Middle East to join a potential mission to protect commercial ships in the Strait of Hormuz once hostilities end.

The ministry said the HMS Dragon will “preposition” in the region, ready to join a UK-and French-led security plan. France announced this week it was moving its aircraft carrier strike group into the Red Sea in preparation.

Britain and France have led meetings involving several dozen countries on a coalition to reestablish freedom of navigation in the strait. But they stress it won’t start until there is a sustainable ceasefire and the maritime industry is reassured ships can go through the strait safely.

In another development, Bahrain, which hosts the US Navy’s regional headquarters, said it arrested dozens of people it alleged had links to Iran’s Revolutionary Guard.

Bahrain said it had arrested 41 people it said are part of a group affiliated with the Revolutionary Guard. The interior ministry said investigations confirmed they were in contact with the Guard and collected funds “with the aim of sending them to Iran” to support its "terrorist operations.”

The small Persian Gulf island is led by a Sunni Muslim monarchy but, like Iran, has a majority Shiite population. Rights groups have said the kingdom has used the war between Iran and the US, which bases its Fifth Fleet in Bahrain, as an excuse to crack down on dissent.

Iran issued a warning to Bahrain: “Siding with the US-backed resolution will bring severe consequences. The Strait of Hormuz is a vital lifeline; do not risk closing it on yourselves FOREVER," Ebrahim Azizi, head of the national security commission of Iran’s parliament, said on social media.

Iran has mostly blocked the critical waterway for global energy since the US and Israel launched the war on Feb. 28, causing a global spike in fuel prices and rattling world markets.

The US has imposed its own blockade of Iran’s ports. US Central Command said on Saturday its forces had turned back 58 commercial ships and “disabled” four since the blockade began April 13.