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 US State Department said on Thursday, according to Reuters.

The UK and Gibraltar seized the Iran-flagged tanker, which was then called the Grace 1, in early July on the grounds that it was attempting to transport oil to Syria.

Gibraltar released the tanker on August 18 after receiving written assurances from Iran that it would not head to countries under EU sanctions.

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 and denied Tehran had broken assurances it gave.

Asked on Thursday 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 the US had evidence of such a transfer from the Adrian Darya 1, Ortagus added, “I wouldn’t say that if we didn’t.”