A leading Iranian Sunni Muslim cleric said that the recent execution of Sunnis could possibly lead to sectarian tensions in the Gulf region, while Tehran allegedly claimed that it was merely taking a tough stance on foreign-backed terrorism.

Iran executed up to 20 Sunnis after accusing them of attacking security forces. There were no public trials and rights groups said the convictions may have been based on forced confessions.

U.N. High Commissioner for Human Rights Zeid Ra’ad Al Hussein said on Friday that “overly broad and vague criminal charges” had led to “a grave injustice”.

“The Islamic Republic of Iran has always taken forceful policy measures to counter regional ‘terrorist’ groups supported by foreign countries,” ministry spokesman Bahram Qasemi was quoted as saying by state news agency IRNA.

Molavi Abdolhamid, a leading Sunni cleric in Iran said the executions lacked “forethought and tolerance” at a time when Iran and the whole region were suffering from extremism.

“Our main complaint is that the sensitive situation in our region has not been considered in these executions,” Abdolhamid, who is regarded as a spiritual leader for Iran’s Sunni minority, said on his website.

Iran has one of the highest execution rates in the world. Amnesty International says at least 977 people were put to death there in 2015, compared to 320 in Pakistan.