An armed wing of Palestinian President Yasser Arafat's Fatah faction has vowed to launch attacks to avenge Israel's killing of six Palestinian militants.
The Al-Aqsa Martyrs' Brigades issued a statement saying they would react, in their words, quickly and painfully with attacks deep inside Israeli territory.
The statement followed Israel's killing of six members of the group during a gun-battle between its troops and Palestinian militants late Sunday in the West Bank town of Tulkarem.
The group, an armed wing of Mr. Arafat's Fatah faction, frequently carries out attacks against Israelis and is listed by the State Department as a terrorist organization.
The Israeli army says that one of those it killed in Tulkarem was Mahdi Tambouz, considered the Fatah leader in the town.
He had been wanted for his alleged involvement in shooting attacks and for organizing suicide bombings. Israel also suspected he had close ties to the militant Islamic group Hezbollah in Lebanon.
The Israeli operation against the Al-Aqsa Martyrs' Brigades in the West Bank coincided with fresh raids by Israeli soldiers into the Gaza Strip.
Palestinians say the Israeli army has effectively taken control over the Beit Hanoun area in northern Gaza. Israeli officials said the operation is aimed at halting the launching of homemade rockets from Gaza against Israeli towns.
At least one Palestinian man was reported killed during an exchange of gunfire between militants and Israeli forces.