The United States has joined a rights group in calling for a full investigation into the death of a Kurdish law student in Iran after he was detained in the western city of Sanandaj.

"The United States is deeply concerned about the tragic death under suspicious circumstances of Ebrahim Lotfallahi, an Iranian student of Kurdish descent detained by the ministry of intelligence on January 6," US State Department spokesman Sean McCormack said in a statement.

"We call on Iranian authorities to conduct a full investigation," McCormack said.

The 27-year-old student's family disputes the official determination that he committed suicide and wants his body exhumed to determine the cause of death, an attorney representing the family said on Sunday.

US-based Human Rights Watch has also called on the Iranian authorities to investigate the "sudden deaths" of Lotfallahi and Zahra Bani-Ameri, a 27-year-old female physician, who died in October while in custody in the town of Hamedan.

In both cases, officials said the cause of death was suicide, the rights organisation said.-Reuters