JERUSALEM -- A militant blew himself up at a Gaza Strip checkpoint and Israeli army fire killed seven Palestinians on Friday, even as Israeli troops withdrew from one West Bank town.

In Jerusalem, the U.N. envoy to the Middle East, Terje Roed-Larsen, said Israel's 3-week-old military campaign in the West Bank created a "dire" humanitarian situation and was largely counterproductive.

The militant Islamic Jihad group claimed responsibility for the suicide bombing at an army checkpoint near the Kissufim crossing between Israel and Gaza, the first such attack in the strip in five months. The assailant was killed and two soldiers were lightly wounded.

In the past 19 months of fighting, scores of suicide bombings have been launched from the West Bank, but none from the Gaza Strip, which is separated from Israel by a high fence. However, the command center of the largest Islamic group -- Hamas -- is in Gaza, which has not been targeted in the Israeli offensive.

In funerals in the strip, supporters of Islamic militant groups and Palestinian leader Yasser Arafat's Fatah movement threatened to carry out new attacks in Israel to avenge more than 200 Palestinians killed.

'Gates of hell'

Leading a procession in Gaza City, a masked Fatah activist told mourners he had a message for Israeli Prime Minister Ariel Sharon: "You have opened the gates of hell .... Murder for murder, and destruction for destruction."

About 2 million people have been under tight closures in the West Bank and Gaza Strip for months, and more than 600,000 have been under around-the-clock curfews for extended periods during the past three weeks, U.N. envoy Terje Roed-Larsen said.

"Israel's operation may have dismantled the physical infrastructure of terrorism, but that is possibly easy to be rebuilt," Roed-Larsen said. "Meanwhile, the mental infrastructure of terrorism is building up, the mentality of hate and confrontation, and this is very difficult to undo."

He said food supplies were dwindling, the water supply was inadequate and suspended garbage collection posed risk of outbreak of disease. He estimated that 75 percent of the work force was now idle.

In the West Bank, a newborn Palestinian baby, 4-day-old Dunya Ishtaya, died en route to a hospital in Nablus Thursday night after the ambulance was stopped at Israeli army checkpoints, the family said Friday.

Nasser Ishtaya, a photographer who covers the West Bank for The Associated Press, said his baby daughter had been born five to six weeks prematurely, and a village doctor said the child had an irregular heartbeat and needed treatment at a hospital. Ishtaya said he spent two hours getting Israeli permission to allow an ambulance to come to their home in the village of Salim 3 miles from Nablus.

The ambulance was stopped at an Israeli military checkpoint outside the village, and Ishtaya said he and his wife, Sareen, 22, were ordered out of the ambulance and searched. While waiting at the next Israeli roadblock, a member of the ambulance crew said the baby had died.

Blaming the army

Ishtaya blamed the Israeli army, saying "the occupation has ruined our dreams." Lt. Col. Olivier Rafowicz, an Israeli army spokesman, said he responded quickly to an appeal from The Associated Press to get permission for the ambulance clear roadblocks and get to the hospital as quickly as possible. He expressed sorrow at the baby's death.

A relief worker said Israeli soldiers refused to let aid organizations deliver food and medicines to the West Bank city of Nablus.

"We got the green light in the morning, but when we got to Nablus it seems the situation had changed," said Peter Holland, of Oxfam Quebec, adding that troops gave no reason for the reversal.

Israeli Defense Minister Binyamin Ben-Eliezer said a gradual withdrawal from Palestinian cities would continue. He said by Sunday morning, troops will have pulled out of Nablus, and of most of the town of Ramallah. Israel has said it will maintain its siege of Arafat's headquarters in Ramallah, where the Palestinian leader is confined to several rooms.

Earlier today, a Palestinian intelligence source said about 25 Israeli tanks were seen pulling out of Ramallah, heading north toward a military base. The Israeli army spokesman's office said there was only "regular military traffic," with no partial withdrawal or military operation in progress.