Iran's rulers have killed at least 300 opposition activists since July in the country's largest wave of political executions since the early 1980s, Amnesty International said Tuesday.

Evidence of the mass executions is indisputable and the true death toll could be in the thousands, the London-based human rights organization said.Opposition activists have been killed secretly in prisons throughout Iran, including Evin and Gohardasht in Tehran and others in Tabriz, Mashhad and Shiraz, Amnesty said.

Iranian authorities initially denied reports of mass hangings and shootings, but Amnesty said the reports were confirmed in effect by public statements in recent days by Iranian officials including President Sayed Ali Khamenei.

Among those executed were people either kept in prison after serving their sentences or rearrested after release, Amnesty said. It added that many of those executed had been tortured.

Most victims were leftists, the majority members of the People's Mujahedeen Organization of Iran, the statement said. It said some were from Rahe Kargar, the People's Fedayeen Organization, the communist Tudeh Party or Kurdish opposition groups.

Both men and women were executed, ranging from students to doctors and clergymen suspected of supporting Ayatollah Montazeri, designated successor to Ayatollah Ruhollah Khomeini, Iran's revolutionary patriarch, Amnesty said.

It cited many sources of evidence, including relatives of executed prisoners and recent statements by authorities. The organization said it had information, all of it cross-checked, on more than 300 executions since July but believed the real number could be in the thousands.