U.S. authorities have moved to seize the cargo of four oil tankers carrying gasoline and fuel products from Iran to Venezuela, escalating a sanctions battle with two regimes Washington opposes and a contest over Iranian oil shipments that allegedly finance its nuclear program.

The action comes weeks after Iran sent five tankers and 1.5 million barrels of gasoline in a symbolic gesture of support to embattled Venezuelan President Nicolás Maduro in defiance of the Trump administration.

A U.S. judge in Washington signed a seizure warrant Thursday for Venezuela-bound shipments aboard four other tankers — the Bella, Bering, Pandi and Luna — whose deliveries were disrupted. Prosecutors estimated their cargo included 1.2 million barrels of gasoline worth nearly $50 million — the seizure of which would be a blow the U.S. government aimed at Iran’s use of third-party shippers to avert economic penalties.

In a civil forfeiture lawsuit and statement filed late Wednesday, U.S. officials in Washington cited a network of informants indicating the fuel was “a source of influence” for Iran’s Islamic Revolutionary Guard Corps, which the United States has designated a terrorist organization. Prosecutors claimed the movements were arranged by Mahmoud Madanipour, an Iran-based man affiliated with the Revolutionary Guard.

Madanipour purportedly acted on behalf of Mobin International Ltd., a firm associated with Guard Corps-connected bank accounts, prosecutors said. Madanipour and the firm also are associated with a United Arab Emirates trading company that the suit did not name that moved to conceal the shipments’ Iranian origin, prosecutors and Homeland Security Investigations agents said.

A text message between Madanipour and a co-conspirator noted difficulties in the voyage of the Liberian-flagged Bella and the Bering, after the United States threatened the Greek owners with possible sanctions, court filings state.

“The co-conspirator texted, ‘the ship owner doesn’t want to go because of the American threat, but we want him to go, and we even agreed We will also buy the ship,’ ” prosecutors wrote in court filings.

U.S. authorities said any funds seized would be directed in part to a fund for U.S. victims of state-sponsored terrorism, according to a statement by the Justice Department’s national security division, the U.S. attorney’s office for the District of Columbia, Homeland Security Investigations and the FBI.

Madanipour could not immediately be reached for comment, and UAE-based Mobin did not immediately respond to requests for comment.

The Iranian mission to the United Nations said the seizure would be “piracy.”

“Any attempt on the high seas to prevent Iran from engaging in lawful trade with any country it chooses will be an act of piracy, pure and simple,” said Alireza Miryousefi, a spokesman for Tehran’s office in New York. “This is a direct threat to international peace and security and in contravention of international law including the U.N. Charter.”

The U.S. move against the tankers is the latest action in a two-year “maximum pressure” campaign of sanctions that have decimated Iran’s economy. And it comes as the Trump administration is making a major push to get support for an extension of a United Nations arms embargo due to expire in October.

Secretary of State Mike Pompeo pressed the U.S. case at the Security Council this week, where he called Iran “the world’s most heinous terrorist regime” and raised fears it could become a rogue arms provider to militant groups throughout the region.

Brian Hook, the State Department’s special envoy for Iran, has just completed meetings in the United Arab Emirates, Saudi Arabia, Bahrain and Israel, where senior officials expressed concern that lifting the embargo could fuel a regional arms race, according to accounts provided by the office of the department’s spokesman.

Hook also went to Vienna on Friday to meet with the head of the International Atomic Energy Agency, a visit designed to highlight a U.S. demand that Iran provide the agency access to suspicious sites where the United States believes Tehran is safeguarding research on developing a nuclear bomb. Iran has repeatedly denied the accusation and called the intelligence behind the charges fabricated.

U.S. officials have tightened sanctions on Iran’s oil industry, a mainstay of its economy, saying the Revolutionary Guard and its major holdings have extensive interests in it and use the profits to support terrorism, proliferation of weapons of mass destruction and human rights abuses.

U.S. sanctions officials assert one network led by the guard’s elite Quds Force in spring 2019 alone used more than a dozen vessels to covertly transport nearly 14 million barrels of crude oil and other petroleum products, grossing more than $750 million.

This week’s actions came almost exactly one year after British authorities seized the Grace 1, an Iranian oil tanker, in Gibraltar, alleging it was carrying oil to Syria in violation of a European Union embargo. Soon after the July 4 incident, Iran detained a British-flagged tanker, the Stena Impero, in the Strait of Hormuz.

Gibraltar ultimately released the Iranian ship in August, despite a last-minute request by the same U.S. attorney’s office in Washington to permit the United States to seize the ship, its oil and $1 million, alleging U.S. sanctions violations.

U.S. authorities in May charged two Iranian men and seized $12 million used to purchase a now-detained Liberian-flagged oil tanker, the Nautic, in what was then billed as the largest seizure of funds used to support the Quds Force.

Washington also hit the five captains of the Iranian-flagged tankers that successfully delivered oil to Venezuela with sanctions.

A State Department official said the sanctions have been effective in depriving Venezuela of its major source of revenue.

“The global shipping community is moving out of doing business with Venezuela in the face of U.S. sanctions,” said Elliott Abrams, the special envoy for Venezuela, in an emailed statement. “The most reputable firms, including the largest Greek shipping companies, have been cooperative and have shown that they value their reputations and their global businesses.”

The Wall Street Journal, which first reported the U.S. disruption of the other Venezuela-bound deliveries of Iranian oil products, has also reported that the Trump administration is preparing to add as many as 50 tankers to U.S. commercial blacklists for working with Maduro’s government.

Wednesday’s court filings state that Madanipour and Mobin International worked with the National Iranian Oil Co. and entities associated with it and the Guard Corps. Madanipour took steps to conceal the involvement of Iranian entities in previous shipments or potential deliveries to China and Malaysia, prosecutors asserted.

For example, the filings state the UAE company, identified only as “Company 1,” in January asked the owner of the Pandi to carry gasoline from Iran to the UAE but that Madanipour changed documents to show that Mobin International was responsible for the voyage. The UAE company then invoiced for $14.9 million an entity that the Guard Corps has publicly said was operating on its behalf and that ran the Grace 1 last year, the filings said.

Prosecutors said Mobin International in March 2019 described setting up a new Persian Gulf country joint venture “to be secured of any risk of sanctions” and “handle all our transshipments of risky oil business.”

According to the court filing, an associate in 2017 also asked Madanipour — allegedly on behalf of proposed Chinese buyers — whether Iranian oil could be provided through other countries with payments made through other countries to avoid U.S. sanctions. “We can get payment in Oman, UAE, Turkey, Italy and Germany,” Madanipour replied, according to court documents.

It was unclear whether the Bella, Bering, Pandi and Luna had been detained. Shipping tracking websites placed the first two Greek-owned vessels most recently in the Aegean Sea, and the other two in the Gulf of Oman.