FILE PHOTO: A crew member takes pictures with a mobile phone on Iranian oil tanker Adrian Darya 1, previously named Grace 1, as it sits anchored after the Supreme Court of the British territory lifted its detention order, in the Strait of Gibraltar, Spain, August 18, 2019. REUTERS/Jon Nazca/File Photo

WASHINGTON (Reuters) - The United States has evidence that the Iranian tanker Adrian Darya 1 has transferred its crude oil to the Syrian government, breaking assurances it gave not to sell crude to the country, the U.S. State Department said on Thursday.

British commandos on July 4 seized the vessel, formerly named the Grace 1, on suspicion that it was en route to Syria in breach of European Union sanctions. Gibraltar released it on Aug. 15 after getting written Iranian assurances that it would not discharge its 2.1 million barrels of oil in Syria.

Britain’s foreign ministry on Tuesday said the tanker had sold its crude oil to the government of Syrian President Bashar al-Assad, breaking those assurances, and that the oil had been transferred to Syria.

Iran’s envoy to Britain, who was summoned by the British foreign ministry over the matter, on Wednesday said Adrian Darya 1’s oil cargo was sold at sea to a private company, denying Tehran had broken assurances it gave. He also said the private buyer of the oil “sets the sale destination.”

Asked if the United States had evidence that the ship had offloaded its crude oil to Syria, State Department spokeswoman Morgan Ortagus told reporters: “Yeah ... The Iranian regime delivered oil to Syria, and that fuel goes straight into the tanks of troops that are slaughtering innocent Syrians.”

Pressed on whether Washington had evidence of such a transfer from the Adrian Darya 1, Ortagus added: “I wouldn’t say that if we didn’t.”

On Tuesday, the State Department had stopped short of confirming whether Iran had sold the oil to Assad’s government, but strongly suggested it had.

The United States, which last year abandoned the 2015 Iran nuclear deal, has imposed severe sanctions on Tehran designed to cut Iran’s oil exports to zero, starve it of resources and force it to accept more stringent limitations on its nuclear and missile programs as well as other regional activities.