The European Union on Thursday questioned the circumstances surrounding the recent death of an Iranian student activist and called on Tehran to launch an independent investigation into the case.

The EU said it was "gravely concerned" about the situation of Iranian human rights activists following the death of Akbar Mohammadi, 34, who died in a Tehran prison on July 31 after a nine-day hunger strike to protest a lack of medical care.

"The circumstances concerning the death of Mr. Mohammadi are also unclear," the EU said in a statement released in Finland, which holds the bloc's rotating presidency. "The EU questions whether Mr. Mohammadi was provided with proper medical care while on hunger strike."

The EU also expressed "grave concern regarding the harsh treatment of dissidents, opposition leaders, student activists and all human rights defenders in Iranian prisons."

Mohammadi, who died in Evin Prison, was arrested for taking part in protests at Tehran University in July 1999 — Iran's biggest anti-government demonstrations since the 1979 Islamic revolution.

He was sentenced to death after being convicted of throwing Molotov cocktails during the protests, but his sentence was later reduced to 15 years in prison.

The Student Committee of Human Rights Reporters of Iran said Mohammadi went on a hunger strike to protest a lack of proper medical care, and had a heart attack.

Prison officials said Mohammadi had been receiving appropriate medical care.

The EU said it had received reports that Mohammadi's trial was "characterized by severe deficiencies" and that he received "inappropriate treatment" in custody.

"The EU asks the Iranian authorities to carry out an independent investigation on the death of Mr. Mohammadi," the 25-member bloc said, adding it will closely monitor the situation of his brother, Manoucher Mohammadi, and other detained Iranian student activists.