Iran seized another oil tanker on May 3, making it the second seizure in under one week. The seizure is adding to concerns that Iran is threatening maritime traffic in the open seas of a pivotal strait where nearly one-fifth of all crude oil passes through.

Surveillance video from the U.S. Navy shows about a dozen of Iran’s paramilitary Revolutionary Guard vessels swarming tanker “Niovi” in the strategic Strait of Hormuz. The tanker was flying a Panama flag.

The aerial drone video shows Guard ships forcing the oil tanker to reverse course and head toward Iranian waters off the coast of Bandar Abbas, Iran.

The drone had been on a routine patrol in the area and captured the seizure, though the Navy did not receive a distress call from the Niovi itself, according to 5th Fleet spokesman Cmdr. Timothy Hawkins.

“Iran’s actions are contrary to international law and disruptive to regional security and stability. 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,” Hawkins said. 

Iran acknowledged the seizure.

According to the Mizan news agency, the prosecutor’s office in Tehran said a judge ordered the Panamanian-flagged tanker impounded over an unspecified complaint. 

This is the second such capture by Tehran amid heightened tensions over its nuclear program. It comes just days after Tehran touted video of another oil tanker bound for the U.S. being captured by Iranian navy commandos.

On April 27, it was reported that Iran seized an oil tanker carrying crude oil for Chevron Corp. of San Ramon, California.

The Advantage Sweet had 23 Indians and one Russian on board. Iran accused Advantage Sweet of colliding with another vessel, but there was no evidence to support the claim.

Iran has a history of reporting unsupported claims when seizing foreign-flagged ships. 

There have been little repercussions, besides condemnation by the U.S. The concern is that Iran could feel emboldened to continue hampering international trade by illegally confiscating oil tankers. Especially in the strait of the Persian Gulf through which one-fifth of all crude passes.

Iran’s seizures are seen as retaliation against the U.S. sanctions placed on the country as a deterrent over its nuclear program. The seizure of oil tankers is just adding to the existing tensions between the U.S. and Tehran.