WASHINGTON (Reuters) - Newly released U.S. court documents show the United States issued a warrant for the seizure of an Iranian tanker that British Royal Marines had seized last month in Gibraltar, citing evidence that it was transporting oil to Syria in violation of U.S. sanctions.

The oil tanker Grace 1, the more than 2 million barrels of oil it carries and $995,000 are subject to forfeiture based on a complaint by the U.S. government, U.S. Attorney for the District of Columbia Jessie Liu said in a news release on Friday.

The tanker was seized by British Royal Marines at the western mouth of the Mediterranean on July 4 on suspicion of violating European Union sanctions by taking oil to Syria, a close ally of Iran.

In a court document obtained by Reuters, it said there was evidence that showed that the tanker was scheduled to arrive in Syria in early July.

“Charts and electronic equipment recovered from onboard the Grace 1, WhatsApp messages recovered from crewmembers’ mobile devices, and crewmembers’ statements revealed that the Grace 1 was destined for Port Banias, Syria in violation of U.S. sanctions,” the document said.

Iran has repeatedly denied that tanker’s destination was Syria.

“As we said earlier ... Syria was not its destination and we have upheld the same ... and reiterated that it was nobody’s business even if it was Syria,” Foreign Ministry spokesman Abbas Mousavi was quoted as saying by Tasnim news agency on Friday.

Gibraltar authorities said on Thursday the U.S. Department of Justice had applied to seize the tanker.

Washington had attempted to detain the Grace 1 on the grounds that it had links to Iran’s Islamic Revolutionary Guard Corps (IRGC), which it has designated a terrorist organization.

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“The scheme involves multiple parties affiliated with the IRGC and furthered by the deceptive voyages of the Grace 1,” Liu said. “A network of front companies allegedly laundered millions of dollars in support of such shipments.”

“A seizure warrant and a forfeiture complaint are merely allegations. The burden to prove forfeitability in a civil forfeiture proceeding is upon the government,” the news release said.

Gibraltar, which said it first received a U.S. Department of Justice request to seize the Grace 1 tanker on Thursday, lifted the tanker’s detention order later in the same day.,

But the vessel’s fate was further complicated by a last-ditch U.S. legal appeal to hold it.

The tanker shifted its position on Friday, but its anchor was still down off Gibraltar and it was unclear if it was ready to set sail soon.

The warrant for the seizure of the tanker, which carries 2.1 million barrels of oil, was issued by the U.S. District Court for the District of Columbia and addressed to “the United States Marshal’s Service and/or any other duly authorized law enforcement officer.”