RAMALLAH, West Bank, Feb 23 (Reuters) - Palestinian President Mahmoud Abbas opened an investigation into the death of a Hamas preacher who the Islamist group said was tortured by Fatah security services, officials said on Saturday.

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.

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 into 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 that an autopsy would be carried out.

A Hamas spokesman blamed Fatah for the death.

"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.

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.

Tension between Hamas and Fatah has increased since the Islamists took control of the Gaza Strip in a brief but bloody civil war in June. Fatah still holds sway in the Israeli-occupied West Bank.

Fatah officials accuse Hamas of torturing Fatah detainees in the Gaza Strip.

Barghouthi's death is the first case of a detainee dying in the custody of Palestinian security forces since Hamas took control of Gaza. (Reporting by Mohammed Assadi and Ali Sawafta; Writing by Ari Rabinovitch in Jerusalem; Editing by Richard Williams)

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