At least 15 people were killed in an attack on a Shia Muslim shrine in the Iranian city of Shiraz on Wednesday, state news agency IRNA said, as security forces elsewhere clashed with protesters marking 40 days since the death of Mahsa Amini.

Early reports of the attack gave varying accounts. The local police chief said there had been a single attacker, who had been arrested, while news agencies said three people were involved.

IRNA described them as “takfiri terrorists”, a label used by officials in predominantly Shia Muslim Iran to refer to hardline, armed Sunni groups. Nournews, affiliated with Iran’s top security body, said they were not Iranian nationals.

The attackers were in a car and shot at pilgrims and staff at the entrance to the shrine of Shah Cheragh, IRNA quoted witnesses as saying. Police arrested two of the three “terrorists” and were looking for the third.

The semi-official Tasnim news agency said several women and children were among the dead.

The attack took place on the same day that Iranian security forces opened fire at mourners who gathered in Amini’s Kurdish home town of Saqez, according to a witness.

“Riot police shot mourners who gathered at the cemetery for Mahsa’s memorial ceremony … dozens have been arrested,” the witness said. Iranian authorities were not available to comment.

Iran’s semi-official ISNA news agency said about 10,000 people had gathered at the cemetery, adding that the internet was cut off after clashes between security forces and people there.

Videos on social media showed thousands of Iranians marching towards the cemetery where Amini is buried despite the heavy presence of riot police. Activists had called for protests across the country to mark 40 days since she died after being detained for “inappropriate attire”.

Demonstrations ignited by the 22-year-old’s death in the custody of Iran’s morality police on September 16 have become one of the boldest challenges to the clerical leadership since the 1979 revolution.

A wide range of Iranians has come out onto the streets, with some calling for the downfall of the Islamic Republic and the death of Supreme Leader Ayatollah Ali Khamenei.

A witness said, “men and women have gathered around Amini’s grave at the Aichi cemetery in Saqez, chanting ‘Woman, Life, Freedom’”. Another witness in Saqez said the cemetery was filled with members of the volunteer Basij militia and riot police.

“But people from all around the Kurdistan province are here. We are all mourning Mahsa’s death together.”

Fearing the 40-day anniversary of Amini’s death would fuel further violent protests, security police had warned her family not to hold a memorial procession or “their son will be arrested”, rights groups said.

However, the governor of Kurdistan, Zarei Kusha, denied there were restrictions on holding a service, adding that it was the family’s decision not to hold a gathering, according to state media.

Videos on social media showed security forces had blocked roads leading to Saqez to prevent people from other cities from gathering at the cemetery. Reuters could not verify the authenticity of the videos.

Authorities closed all schools and universities in the Kurdistan province on Wednesday “because of a wave of influenza”, Iranian state media reported.