France and Britain are calling on Iran to explain the death in detention of an anti-government blogger who opposition activists say had been tortured.

Activists say 35-year-old Sattar Beheshti was arrested in his home in late October, and that his family was asked on Wednesday to pick up his body from a detention center in Tehran.

In his last posting before being arrested, Beheshti wrote that security services had threatened him — saying his mother “would soon be wearing black” if he continued speaking out.

Officials in France and Britain said they were shocked by reports of Beheshti's death. The British Foreign Office said it appeared to be another attempt to crush any form of free expression in Iran.

Iranian officials have not commented on his detention or cause of death. Beheshti's sister, Fatima, told Voice of America's Persian News Network that her brother did not have any history of illnesses.

Human rights groups Amnesty International and Reporters Without Borders are also calling on Iran to release details of his death.