Human right activists and relatives called for a probe Tuesday into the sudden deaths of two Iranians who were in government custody, rejecting official claims that the two committed suicide.

The government has refused to provide additional information about the circumstances surrounding the deaths of Zahra Bani Yaghoub and Ebrahim Lotfollahi or even tell their families why they were arrested, leaving relatives distraught.

"There was no reason for my sister to commit suicide. How can I believe the (government's) claim?" said Rahim Bani Yaghoub, whose 27-year-old sister, a doctor, died in prison in the Western Iranian town of Hamedan on October 13, a day after she was arrested by anti-vice police while walking in the park with her fiance.

Rahim said his sister's fiance was released an hour later, but Zahra was kept overnight. The next day, her lifeless body was handed over to her family with "bruises on her thigh and legs," he added.

"We want to know what are the causes for the bruises on her body," Rahim said during a press conference Tuesday in Tehran, as tears rolled down his cheeks.

"There are lots of contradictions in the government's claims over the circumstances," Rahim said.

Equally frustrated is the family of Ebrahim, a 27-year-old student who died in a detention center in the western Iranian city of Sanandaj sometime between January 9 and January 15.

"We still don't know how my brother died," said Esmaeil Lotfollahi. "We took our complaint to court but my parents were insulted by court authorities."

Esmaeil said security agents arrested his brother on January 6 as he was leaving the Sanandaj campus of Payam Noor University. Authorities allowed Esmaeil and his mother to visit Ebrahim at the Sanandaj detention center three days later, but refused to tell them the charges against him.

On January 16, authorities contacted the family again to show them a grave where they said Ebrahim was buried, raising Esmaeil's suspicion that his brother was murdered.

"If authorities are telling the truth, why didn't they even show the body to us before his secret burial?" said Esmaeil, appearing at the press conference alongside the Bani Yaghoub family.

Nobel laureate Shirin Ebadi, who is representing the Bani Yaghoub and Lotfollahi families in their lawsuit against the government, said she doesn't believe the official claim the two committed suicide.

"Even if we are to believe the official version, we need to ask how the authorities treated our youth that forced them to kill themselves," she said.

Narges Mohammadi, a human rights activist, said her group wants those responsible for the tragedy to be brought to justice.

"We want the authorities to identify and bring to justice those responsible for the tragic deaths," she said.