Palestinian ex-security chief Moussa Arafat has been shot dead in Gaza after being dragged from his home by gunmen.
Moussa Arafat's body was dragged from his villa
The cousin of the late leader Yasser Arafat is the most senior figure to be killed in internal violence that has gripped the Palestinian territories.
The attack has been claimed by a militant splinter group, the Popular Resistance Committees.
They battled his bodyguards for half an hour, before killing Arafat outside his house and abducting his son.
Palestinian leader Mahmoud Abbas said everything would be done to catch the killers and free Manhal Arafat.
"This assassination will not undermine our efforts to impose law and public order," he said in a statement.
PRC spokesman Abu Abir said the attack against "the collaborator" Arafat and kidnapping of his son were undertaken "for reasons to be announced later".
Correspondents say Gen Arafat, who was sacked as Gaza security chief earlier this year but reappointed as presidential security adviser, made many enemies in a long career in the security forces.
The 65-year-old had been accused of corruption.
The BBC's Alan Johnston in Gaza says his assassination is another indication of the tensions and lawlessness in Gaza, as the Israelis withdraw from the territory.
Mr Abbas has called an emergency meeting of his security commanders and Prime Minister Ahmed Qurei, as the hunt for the gunmen begins.
About 20 cars carrying masked men are believed to have encircled the villa in the south of the city.
The attackers shot rocket-propelled grenades at Gen Arafat's house, and his bodyguards returned fire.
The gunmen then entered the building and shot the former security chief. Blood stained the street where his body was left.
A Palestinian minister told the BBC the authorities were shocked by the killing, and were trying to impose order in Gaza.
"It's a court of law that should have addressed this matter," Sabri Saidam said.
"The authorities should have brought Mr Arafat to question, rather than see the scene which took place in Gaza this morning."
The PRC is a coalition of Palestinian militant groups. The group is made up mostly of former members of Mr Abbas' Fatah political movement, with militants from Hamas and Islamic Jihad. It has taken responsibility for many attacks on Israelis.
Our correspondent says Moussa Arafat was a controversial figure, who had survived earlier attempts on his life.
The late Yasser Arafat's attempt to put his cousin in overall charge of Palestinian security in July 2004 sparked violent demonstrations.
Elements within Fatah objected to the appointment, alleging that he was corrupt.
He had become widely unpopular among Palestinians, who view him as one of the "old guard" and steeped in corruption.
As chief of military intelligence in the 1990s, Gen Arafat earned a reputation for ruthlessness.
He was involved in a 1996 crackdown on Hamas and Islamic Jihad militants, when he shaved the heads and beards of detainees as a form of humiliation.