Iran's ambassador to the United Kingdom has signaled little progress toward a negotiated settlement to a standoff over captured oil tankers. "Impossible to advance a quid pro quo or barter exchange of detained UK and Iranian ships," Hamid Baeidinejad tweeted July 29.

Baeidinejad reaffirmed Tehran's official line that the UK detention of the Iranian vessel Grace 1 off Gibraltar was "illegal" while Iran's capture of the Stena Impero was a response to violations of "some key safety/security regulations" by the British-flagged ship in the Strait of Hormuz, the strategic maritime pathway for 20% of global oil.

The ambassador's post appeared to have come in reaction to UK Foreign Secretary Dominic Raab, who earlier ruled out any exchange deal with the Iranian side. “There is no quid pro quo. Grace 1 was intercepted because it was in breach of sanctions and heading with oil to Syria,” Raab told BBC Radio on July 29.

Last week, Iranian President Hassan Rouhani spoke of a "proportionate response" from Tehran if London releases the Iranian tanker. The comment was widely interpreted as an exchange offer. Later, Kamal Kharrazi, a veteran diplomat and the director of Iran's Strategic Council for Foreign Relations, said that if Britain freed the Iranian vessel, Iran "would accelerate the due legal process" of releasing the British one.