The U.S. government has applied to seize an Iranian oil tanker impounded in Gibraltar last month, the government of the British overseas territory said on Thursday.
"U.S. Department of Justice has applied to seize the Grace 1 on a number of allegations which are now being considered," Gibraltar officials said in a statement sent to NBC News.
They said the case will return later in the day to Gibraltar’s Supreme Court, which was already due to rule on the matter on Thursday.
NBC News has requested comment from the Department of Justice. There was no immediate reaction from Tehran.
Gibraltar officials also said the tanker crew members initially arrested, the captain and three officers, have now been released.
Their whereabouts are not presently known.
Grace 1 was seized last month in a British Royal Navy operation off of Gibraltar. It is suspected of violating European Union sanctions on oil shipments to Syria, an ally of Iran and its seizure deepened international tensions in the Persian Gulf.
Just weeks later, Iran seized a British oil tanker named Stena Impero in the Strait of Hormuz for "violating international regulations."
Earlier this week, Britain's Foreign Office announced that "investigations being conducted around the Grace 1 are a matter for the government of Gibraltar." A spokesman for the Foreign Office told NBC News on Thursday that they have not issued any further guidance or response to the U.S. move.
Tensions have escalated in the region since President Donald Trump unilaterally withdrew the U.S. from Iran's 2015 nuclear deal with world powers over a year ago.
The decision stopped billions of dollars' worth of business deals, largely halted the sale of Iran's crude oil internationally and sharply depreciated Iran's currency.
In recent weeks, Iran has begun to step away from the nuclear deal by increasing its production and enrichment of uranium. It has threatened to take further steps in early September if Europe can't help it sell its oil abroad.