GAZA - Hamas Islamists detained an adviser to President Mahmoud Abbas's government and three Fatah mourners were killed in an explosion on Friday, fuelling tensions between rival Palestinian factions in the Gaza Strip.

Hamas said its forces took Omar al-Ghoul, a senior adviser to Prime Minister Salam Fayyad, from his home in the highest-profile detention since the group seized the coastal strip in June after routing Abbas's secular Fatah faction.

Abbas and Fayyad's government condemned the abduction and accused Hamas of setting off an explosion that ripped through a funeral procession for three militants. They had been killed in an Israeli air strike on Thursday.

Medical officials said at least three Fatah mourners were killed and 35 were wounded in Friday's funeral blast.

Hamas security officials said a mourner taking part in the procession accidentally dropped a grenade into the crowd. Hamas spokesman Sami Abu Zuhri told a news conference Hamas "had him", although he declined to name the suspect.

Factional tensions rose as Hamas prepared to mark the 20th anniversary of the group's founding with mass rallies in Gaza on Saturday.

Hamas said similar demonstrations have been banned by Abbas in the occupied West Bank, where Fatah holds sway.

Abu Zuhri accused Fatah of trying to "poison the atmosphere" ahead of Saturday's Hamas rallies and called on Hamas leader Ismail Haniyeh to order the banning of Gaza rallies by Fatah for their anniversary day on January 1.

ANNIVERSARY

Saturday's rally is to be held at the spot where last month seven Fatah supporters were killed by gunfire while commemorating the third anniversary of the death of iconic Palestinian leader Yasser Arafat.

Abbas's office issued a statement saying: "What happened was an assault against all our people."

Haniyeh ordered an investigation, but he accused his Fatah rivals of trying to destabilise Hamas's rule of the Gaza Strip.

Ghoul had been living in the West Bank city of Ramallah where Fayyad's government is based. He was taken into custody by Hamas a day after arriving in Gaza to attend the funeral of his mother-in-law, his family said.

A spokesman of the Hamas-run Interior Ministry, Ehab al-Ghsain, said: "We have detained Ghoul and he is being investigated over violations to the law." The spokesman declined further comment.

Fayyad's information minister, Riyad al-Malki, called for Ghoul's immediate release.

"Hamas and all of its parties are responsible for his life," Malki said, calling the abduction a message to Fatah leaders that "Gaza is closed to them".

Ghoul is a well-known columnist for local newspapers and a frequent critic of Hamas.

Abbas responded to the takeover of Gaza in June by dismissing Haniyeh and his Hamas-led government and appointing Fayyad to run a Western-backed administration in the occupied West Bank.

Hamas leaders have offered a long-term truce with Israel in return for a viable Palestinian state in the occupied West Bank and the Gaza Strip. But the Islamist group continues to say it will not formally recognise Israel and its 1988 founding charter calls for the destruction of the Jewish state.