Hamas Islamists have accused security agents from Abbas's more secular Fatah faction of torturing to death imam Majd al-Barghouthi, a local Hamas leader in the West Bank city of Ramallah, near Jerusalem.
Abbas's security force said on Friday that Barghouthi had died of a stroke. The 45-year-old father of nine had been detained for a week before his death.
"President Abbas has demanded the attorney general investigate ... the issue and give a report as soon as possible," the official WAFA news agency said.
The head of a local hospital to which Barghouthi was taken said he was dead when he arrived there.
"The man who arrived at the hospital was already dead," physician and hospital manager Jamal al-Tarifi said.
Tarifi declined to say whether doctors had observed any signs of violence on the body and said an autopsy would be carried out.
"We consider this a grave event that reflects the ugly crimes Abbas's forces commit against Hamas," the faction's spokesman Sami Abu Zuhri said in Gaza.
A statement issued by the Islamist group said Abbas's decision to order an investigation was "throwing sand in the eyes" of the public and held Abbas, Prime Minister Salam Fayyad and intelligence chief Tawfiq Tirawi responsible for the death.
On Friday, members of the Barghouthi clan closed a major West Bank road near Ramallah, rioted and set ablaze tyres in protest at the death.
Güncelleme Tarihi: 24 Şubat 2008, 15:23