DUBAI (Reuters) - The head of Iran's prisons apologised on Tuesday for "bitter events" in Tehran's Evin prison after videos leaked by hackers showed beatings of prisoners, a rare admission of abuse by authorities.

       A hacking group calling itself Edalat-e Ali (Ali's Justice) issued on social media the videos that appear to be from the prison's surveillance cameras and show guards beating prisoners and dragging a detainee on the floor.

       "Regarding the pictures from Evin prison, I accept responsibility for such unacceptable behaviour and pledge to try to prevent any repeat of these bitter events and to deal seriously with the wrongdoers," Mohammad Mehdi Hajmohammadi, head of Iran's prisons, said in a tweet reported by state media.

       "I apologise to God Almighty, our dear leader (Supreme Leader Ayatollah Ali Khamenei), the nation and honorable prison guards, whose efforts will not be ignored due to these mistakes," Hajmohammadi said.

       It was a rare admission of human rights abuses in Iran, which often has dismissed criticism of its human rights record as baseless.

       Evin prison, which mostly holds detainees facing security charges, has long been criticised by Western rights groups and it was blacklisted by the U.S. government in 2018 for "serious human rights abuses".

       "The (Evin) authorities use threats of torture, threats of indefinite imprisonment and torture of family members, deception and humiliation, multiple daily interrogations lasting up to five or six hours, denial of medical care, and denial of family visits," Human Rights Watch said in a report.

       In July, Iran faced cyberattacks on the website of its transport ministry and the state railway company.

       (Reporting by Dubai newsroom, Editing by Angus MacSwan)