“We know for certain it is many, many hundreds,” Brian Hook, the U.S. special representative for Iran, told reporters in Washington on Thursday. “Perhaps over 1,000. This is the worst political crisis the regime has faced in its 40 years.”

Hook said at least 7,000 protesters have been detained in a network of prisons that the Trump administration intends to sanction, adding that Secretary of State Michael Pompeo has determined they are responsible for gross human rights violations. Hook dismissed assertions from Iranian officials that protests in about 100 cities in Iran have had anti-American bias.

Iran acknowledged for the first time this week that its security forces shot and killed protesters last month during one of the most violent crackdowns on dissent since the 1979 Islamic revolution. State television on Tuesday reported that “rioters” had been shot dead in several areas as they joined anti-government protests, including in Tehran, the capital, and Mahshahr in the country’s southwest.

The protests — sparked by an surge in gasoline prices — come as President Hassan Rouhani’s government is under increasing pressure from U.S. sanctions that have hammered the Islamic Republic’s economy. The International Monetary Fund expects Iran’s recession to deepen this year, with gross domestic product contracting 9.5%.

The Islamic Revolutionary Guard Corps said on Saturday that it was investigating reports that its forces had targeted and shot protesters, the semi-official Iranian Labour News Agency reported, citing Brigadier General Mohammadreza Yazdi.

Hook also announced Thursday that the U.S. will offer $15 million for information on the whereabouts and activities of an Iranian commander based in Yemen, who he said “has a long history of attacks against Americans and our allies globally,” including a planned effort to assassinate the Saudi Arabian ambassador to the U.S. in 2011.

DM