Israel closed off the West Bank and Gaza for the Jewish Passover holiday on Friday, a day after Gaza militants attacked a vital crossing, raising the possibility of a large-scale Israeli offensive within weeks.

The closure, which went into effect in the early morning, was to last until the end of the holiday on April 26, according to a statement from the military. Palestinians are banned from entering Israel, except for doctors and lawyers and in humanitarian cases, it said.

The military regards the holiday period "as a highly sensitive time, security wise," the statement said. The military "will increase its alertness ... while preserving, to the best of its ability, the daily life of the Palestinian population," it said.

In violence Friday, Israeli troops killed a militant leader during a raid on the West Bank city of Nablus, the Al Aqsa Martyrs' Brigades group said. Another militant from the Islamic Jihad was seriously wounded, medics said.

Israel's army confirmed that a militant had been killed in an operation in Nablus, saying he fired at troops from a rooftop when they surrounded a house in an effort to arrest him.

The man killed was Hani Al-Kabi, a leader of Al Aqsa in the Balata refugee camp who fled a Palestinian jail with about a dozen militants three months ago. The militants accused Israel of reneging on an amnesty deal.

Kabi was wanted for several attacks that were thwarted, including a recent attempted poisoning at a restaurant, and for a shooting in which two soldiers were wounded, the army said. Al Aqsa denied Kabi was involved in the poisoning plot.

The Israeli operation in Nablus suggested an Israeli-Palestinian understanding on security in the militant stronghold was unraveling. Israel had earlier this year agreed to the deployment in the city of Palestinian security forces allied with moderate President Mahmoud Abbas. But Israeli troops have continued to operate there almost nightly.

Nablus is considered a test case for plans for further deployments of Palestinian forces around the West Bank — a key component of peace talks renewed last year and Abbas' effort to take charge of the territory in facing his rival, the Islamic Hamas group. Hamas rules the Gaza Strip since seizing control from Abbas-allied forces in June.

Israel's army promised, despite the closure of Gaza and the West Bank, to continue transferring vital goods through Gaza crossings.

But at the time the army statement was released late Thursday, two of the main crossings were closed: Kerem Shalom, through which Israel transports food and medicine, and the fuel depot at Nahal Oz — because of attacks by Palestinian militants.

Israeli troops fended off Palestinian gunmen who assaulted Kerem Shalom on Thursday, killing one, and then militants opened fire again at Nahal Oz.

The renewed violence followed a day of fighting between Israeli forces and Gaza militants that killed three Israeli soldiers and 21 Palestinians, including five children and a news cameraman.

Gazans are angry over a nearly yearlong blockade of their borders, causing shortages in almost all commodities in the seaside territory, and Israel generally halts all shipments after attacks like Thursday's.

With Egyptian efforts to mediate a Gaza cease-fire sputtering, Hamas has repeatedly threatened to violently break through the Israeli border. The group blew up the wall along Gaza's border with Egypt in January.

Israel has greatly restricted the flow of fuel and goods into Gaza because of repeated rocket attacks by Gaza militants on southern Israel. Israel considers Hamas a terrorist group. Gaza militants consider the border crossings humiliating symbols of the economic blockade.

Israeli defense officials said it would likely be a few weeks before Israel carries out any broad operation in Gaza, because of next week's Passover holiday and the country's 60th anniversary celebrations next month.