Iran’s paramilitary Revolutionary Guard has seized a Panamanian-flagged oil tanker in the strategic Strait of Hormuz, the second such capture in less than a week.

The taking of the Niovi renewed concerns about Iran threatening maritime traffic in the strait, the narrow mouth of the Persian Gulf through which a fifth of all crude oil passes.

It also comes amid the disappearance of a tanker in south-east Asia believed to have been carrying Iranian crude oil amid reports it may have been seized by the US.

The US Navy published surveillance footage shot by an aerial drone of about dozen Guard vessels swarming the tanker on Wednesday morning. The drone had been on a routine patrol in the area and saw the seizure, though the Navy did not receive a distress call from the Niovi, 5th Fleet spokesman Commander Timothy Hawkins said.

The Guard ships “forced the oil tanker to reverse course and head toward Iranian territorial waters off the coast of Bandar Abbas, Iran”, the Navy said.

“Iran’s actions are contrary to international law and disruptive to regional security and stability,” the 5th Fleet said in a statement.

“Iran’s continued harassment of vessels and interference with navigational rights in regional waters are unwarranted, irresponsible and a present threat to maritime security and the global economy.”

Iran acknowledged the seizure, with the judiciary’s Mizan news agency quoting the Tehran prosecutor’s office as saying that a judge had ordered it impounded over an unspecified complaint.

Shipping registries show the Niovi as managed by Smart Tankers of Piraeus, Greece. The Niovi had been coming from dry-dock repairs in Dubai, bound for Fujairah on the eastern coast of the United Arab Emirates without carrying any cargo, according to data firm Refinitiv.

Last week, Iran seized an oil tanker carrying crude for American firm Chevron, amid wider tensions between Tehran and the US over its nuclear programme. The Advantage Sweet had 23 Indians and one Russian on board.

Iran has accused the Advantage Sweet of colliding with another vessel, but offered no evidence to support its claim. Iran has offered a variety of unsupported claims in the past when seizing foreign-flagged ships amid tensions with the West.

The taking of the two tankers in under a week comes amid the disappearance of the Marshall Island-flagged Suez Rajan, which had been in the South China Sea off Singapore for over a year after a report alleged it was smuggling sanctioned Iranian crude oil.

Tracking data for the Suez Rajan last showed it off east Africa, moving in a direction that could take it to the Americas.

The Financial Times and maritime intelligence firm Ambrey reported the Suez Rajan was seized on order of American authorities.

The Greek Ministry of Maritime Affairs acknowledged on Wednesday that it had recently sent a warning to Greek ships in the Middle East to be on alert when going through the Persian Gulf. The ministry did not say what prompted the warning.

The seizure by Iran of two ships in the last week was the latest in a string of ship seizures and explosions to hit the region.

The incidents began after then-president Donald Trump unilaterally withdrew the US from Iran’s nuclear deal with world powers, which saw Tehran drastically limit its enrichment of uranium in exchange for the lifting of economic sanctions.

They have continued under President Joe Biden as diplomatic efforts at finding a way back to the accord remain in stalemate.