At least seven prisoners were hanged on Thursday in a prison in the southern city of Shiraz.
The prisoners who had been arrested on drug related charges were hanged in the city’s main prison known as Adelabad prison.
The victims had been transferred to Isolation last Thursday, a day before the Iranian New Year and hanged in secret this week.
Many prisoners have been hanged secretly during the last few months in prisons across Iran.
According to a report, a group of four men also were hanged last month in a prison in the city of Maragheh, in northwestern Iran.
They were identified as Bahram Ashtari, Atef Ranjbar, Karim Sadat and Vali Najafnia.
Some 1,400 individuals have been executed in Iran under Hassan Rouhani. The victims included political prisoners, women, juvenile offenders and citizens of Afghanistan.
The U.N.'s special investigator on Iran said on March 16 that the human rights situation and repression of Iranian women and activists has worsened since Hassan Rouhani became president in 2013.
Dr. Ahmed Shaheed said in Geneva: "in my view the overall situation has worsened, as indicated by the surge in executions."
He lamented that Iran executes more people per capita than any other country in the world.
"There is a lot of concern amongst the Iranian society that the nuclear file may be casting a shadow over the human rights discussion," Shaheed told the news briefing.
Mr. Shaheed, a Muslim and former foreign minister of the Maldives, has not been allowed to visit Iran since taking up the independent post.