WASHINGTON - U.S. lawmakers from both political parties have urged President Joe Biden and members of his administration to resolve a months-long delay in the transfer of a cargo of oil from a seized Iranian tanker off Texas.

The Suez Rajan has been stuck near Galveston about 50 miles (80 km) from Houston since May 30, as shipping companies fear any vessel unloading it would lead other oil buyers to shun their ships on future voyages. The U.S. seized the tanker in a sanctions enforcement operation.

The delay in discharging the cargo is also partly out of fear of repercussions from Iran. A senior commander of Iran's Revolutionary Guards' navy said last month Iran would retaliate against any oil company unloading Iranian oil from a seized tanker.

Senators Joni Ernst, a Republican, and Richard Blumenthal, a Democrat, and other lawmakers in the Senate and U.S. House said in the letter to Biden and senior administration officials that enforcement of petroleum sanctions will become irrelevant if American citizens and companies involved constantly live in fear of Iranian retaliation.

"It is imperative that the Administration make clear that Iran and designated Foreign Terrorist Organizations cannot prevent our government from carrying out legitimate law enforcement operations," the lawmakers said in the letter sent late on Tuesday and seen by Reuters.

They asked the administration for a briefing on the progress of the transfer of the seized oil from the Suez Rajan to U.S. custody.

The White House did not immediately respond to a request for comment.

The saga of the tanker is occurring as Washington and Tehran seek a deal to free five detained U.S. citizens in exchange for releasing $6 billion in Iranian funds frozen in South Korea. A deal would remove a major irritant between Washington and Tehran, which are at odds on issues from the Iranian nuclear program to Tehran's support for regional Shi'ite militias.

The lawmakers estimated the value of the oil on the 800,000 barrel tanker to be $56 million. U.S. seizures of Iranian oil contribute money to the U.S. Victims of State Sponsored Terrorism Fund, which compensates victims of attacks. A fund official has determined there are insufficient assets for a round of payments next year to the nearly 16,000 Americans.

(Reporting by Timothy Gardner; editing by Grant McCool)