Iranian Ayatollah Ali Khamenei gestures before delivering a speech in Mashad, on March 21, 2018. Photo: Leader.ir / Handout via Reuters.

A large number of prisoners in Iran will be pardoned on Thursday in honor of the 40th anniversary of the revolution that toppled the US-backed shah, Ayatollah Ali Khamenei said on his Twitter account.

The number of prisoners that will be pardoned by Khamenei was not announced, but Iranian media earlier said around 50,000 prisoners will enjoy “the Islamic clemency.”

The country is holding official celebrations for the anniversary of the 1979 Islamic Revolution that will culminate next Monday in a nationwide rally.

It was not immediately clear whether those who will be pardoned will include some of the hundreds of prisoners that human rights groups say have been jailed for political offenses.

Several dual nationals from the United States, Britain, Austria, Canada and France have been detained by Iran’s security forces in past years and have been kept behind bars on charges including espionage and collaborating with hostile governments.

Khamenei has the final say on all state matters and issues pardons or reduces sentences of prisoners on special occasions.