Security forces inspect the scene of the shoot-out
Six people have been killed in a West Bank clash between Hamas fighters and Palestinian policemen, officials say.
Three policemen, two members of Hamas and another man were killed in a gun battle when police went to arrest the Hamas men in a dawn raid in Qalqilya.
Officials said the police were loyal to Palestinian leader Mahmoud Abbas, of rival group Fatah.
It is one of the worst clashes in the West Bank since Hamas seized control in the Gaza Strip in 2007.
The owner of a home in which
gunmen had been hiding was also killed, Palestinian security officials said, according to Reuters news agency. Factional tension
Fighting erupted when police went to arrest Mohammed al-Samman, the commander of Hamas's armed wing in the northern West Bank, reports said.
Mr Samman and another Hamas man, had ignored calls to surrender, witnesses told Reuters.
Aleem Maqbool, BBC News, Ramallah
For nearly two years, Hamas has been in charge of the Gaza Strip, and Fatah, the West Bank.
During that time both sides have been accused by human rights groups of abuses of power against rival supporters - including arbitrary arrests and even torture.
But Fatah says this incident was simply a case of trying to enforce the law. That hasn't stopped it raising tensions.
The two factions are supposed to be in a reconciliation process to end their deep split.
But their talks seem to be going nowhere. Mistrust between them remains high.
And the power struggle, which has been so damaging to Palestinian society and the national cause, looks set to continue.
Palestinian security forces spokesman Adnan Damiri said "thousands" of shots had been fired at Palestinian security forces during the battle.
Hamas responded to the shooting with a statement from Gaza denouncing Mr Abbas's forces as "Zionist agents".
"Their crackdown against and pursuit of wanted men with the help of the enemy [Israel] lays down the foundation for resistance" by Hamas, Reuters reported the group as saying.
Fatah denied the Hamas claim, saying it was simply a case of trying to enforce the law.
There are now fears of tit-for-tat arrest campaigns in the West Bank and Gaza, as has happened in the past, says the BBC's Aleem Maqbool in Ramallah.
Inter-factional fighting in Gaza came to a head in the summer of 2007 when Hamas fighters ousted the pro-Fatah security forces and overthrew Palestinian Authority control.
As well as continued tension, both sides have been accused of conducting politically motivated arrests and the
torture of rival faction members
Solving Fatah-Hamas differences is seen as an essential step if an Israeli-Palestinian peace deal is to happen.
Unlike the Fatah-dominated PLO, Hamas refuses to recognise Israel's right to exist and has waged a violent campaign against it for years.