RAMALLAH ø Israel has assassinated a leading Fatah insurgent in the West Bank.

Israeli and Palestinian sources identified the insurgent as Halil Muhamed Zuhaid Araysha, 24, the leader of the Fatah-dominated Al Aqsa Martyrs Brigade in the Balata refugee camp outside of Nablus. Araysha was said to have planned 20 suicide bombing attempts in Israel.

Two aides of Araysha were also killed in the Israeli helicopter attack. They were not immediately identified.

"The Israel Air Force targeted a vehicle carrying a senior Tanzim [Fatah] terrorist, who is responsible for several terrorist attacks against Israeli civilians and IDF soldiers," a military statement said. "After repeated efforts to arrest the terrorist were to no avail, the IDF acted in order to thwart future attacks."

Israeli sources said the latest attempt was a plot to bring a car bomb into Jerusalem earlier this month. They said not one of the bombing attempts was successful.

Araysha was said to have operated with two other Fatah operatives in Balata ø Nader Abu Lil and Hashem Abu-Hamdan ø in attacks against Israeli soldiers and Israeli communities in the Nablus area as well as civilian targets in the Jewish state. Abu Lil and Abu Hamdan were killed in an air force missile strike in May 2004.

Araysha and two other Fatah insurgents were killed in an Israeli helicopter strike on late Monday in Balata, Palestinian sources said. They said Araysha was believed to have been financed by the Iranian-sponsored Hizbullah. Later, Israel's military reported that a combat unit found a weapons cache in Nablus that included four bombs, four assault rifles, a mortar shell, explosives and a rocket-propelled grenade. The military said the bombs and explosives were destroyed.

Over the last month, Araysha was planning mass-casualty attacks against Israeli civilian targets. On June 3, Israeli authorities foiled an attempt by Araysha to send a suicide bomber into Jerusalem. In May, he was said to have directed a suicide car bombing attack against a military outpost near Nablus. Israeli military sources said the attack was thwarted because authorities had obtained advanced information.

On Sunday, Palestinian sources said Israel's military tried to kill the Al Aqsa commander in Jenin, identified as Zakarai Zubeidi. The sources said the Israeli attack failed.

Israeli officials said authorities also foiled a Hamas plot to bomb the office of Prime Minister Ariel Sharon. They said a Hamas operative, identified as Husam Nabulsi, sought to place a bomb into stationary supplies delivered to Sharon's office.

Nabulsi, officials said, worked as a driver for an Israeli printing company that delivered the stationary supplies and other printing material to the government office. They said the bomb was to have been detonated by a cellular phone.

"The intention of infiltrating the bomb into the Prime Minister's Office arose in light of Nabulsi's job as a driver for an Israeli company in Jerusalem, which involved access to various government offices including the Prime Minister's Office," a government statement said.

In May, Nabulsi, 38, was arrested as part of a Hamas plot to carry out a mass-casualty attack in a Jerusalem neighborhood. Officials said Hamas tried and failed to bring a huge bomb into one of the city's synagogues. They said Israel's security fence limited Hamas's options.

"The construction of the terrorism prevention fence has led terrorist infrastructures in Judea and Samaria, especially the latter, to use eastern Jerusalem as a base from which to perpetrate attacks at attractive targets," the Israeli statement said.