By making that link, Iran appeared to be trying to press the Europeans to make good on the promised financial benefits of the 2015 agreement known as the Joint Comprehensive Plan of Action, or J.C.P.O.A.

“Since Iran is entitled to export its oil according to the J.C.P.O.A., any impediment in the way of Iran’s export of oil is actually against the J.C.P.O.A.,” Iran’s deputy foreign minister, Abbas Araghchi, said after emergency talks in Vienna with other parties to the nuclear deal.

Reminder: British forces impounded the Iranian tanker in early July near Gibraltar, accusing it of violating E.U. sanctions on Syria, an act Britain said had nothing to do with the nuclear deal.

On July 19, Iranian commandos seized a British-flagged tanker in the Strait of Hormuz, the world’s most important waterway for oil shipments, arguing that it had committed violations but formally denying that it was a tit-for-tat response.

Barter system: European officials said a long awaited alternative trading platform, which would allow Iran to bypass the American-linked global financial system and avoid new sanctions, is in its final stages (but they have said this for months).