Fearing that militants would re-enter Bethlehem's Church of the Nativity, IDF forces drove into the adjacent Manger Square early Monday, blocking off access to the church complex, an Israeli military source said.

In a separate IDF operation in the Gaza Strip, Palestinian sources reported that a 17-year-old youth was killed by Israeli tank fire.

Witnesses and Palestinian security sources said dozens of jeeps and armored troop carriers entered Bethlehem and the neighboring Deheisheh refugee camp in the pre-dawn hours Monday, in the army's second raid into the West Bank city since Saturday.

The IDF imposed curfews on the neighborhoods of a Doha and Ta'amra and arrested dozens of terror suspects in the area.

The army said the new raids were designed to "safeguard the gains" of a more than month-long offensive in the West Bank.

Israel Radio reported that troops in Deheisheh arrested a senior member of the Fatah Al Aqsa Brigades. It identified the man in custody as Ahmad al-Mughrabi, saying that he was one of the most wanted Palestinian fugitives in the area, and was linked to a number of deadly attacks in the Jerusalem area.

Al-Mughrabi's brother Ali was also arrested Monday, together with another wanted Palestinian, Mahmoud Sirhana. According to the Shin Bet security service, the three orchestrated the Rishon Lezion suicide bombing last week, in which two Israelis were killed.

Also arrested was the sister of the young woman suicide bomber who attacked a Jerusalem supermarket as part of a wave of attacks during the Passover holiday.

IDF Chief Spokesman Ron Kitrey said the increasing number of warnings of suicide bombings launched from the West Bank "is of great concern. It compels us to be taut like a spring in every place from Jenin in the north to Hebron in the south."

Troops also maintained a military grip on Qalqilyah on Monday as the army intensified raids into Palestinian areas after four suicide bomb attacks last week.

Soldiers in jeeps drove into Manger Square at the heart of the city before dawn, and closed off access to the Church of the Nativity, which sits on the spot revered as the place where Jesus was born, an Israeli military source said. The Israeli source said the measure was taken "so the terrorists would not escape" to the church.

The church was the site of a five-week standoff between Israeli troops and Palestinian gunmen lifted early this month when 39 militants inside who were wanted by Israel agreed to go into exile in Europe or to the Gaza Strip.

In the Gaza Strip, Palestinian sources said armored troops operating in the Khan Yunis area fired a tank shell that killed Muhammad Abu al-Hir, 17, a resident of the area. The sources said al-Hir died of his wounds before reaching a hospital.

There was no immediate IDF comment on the incident.

Israeli military commentators have described the overlapping raids as a less risky way of searching for suicide bombers after Israel ended a broad West Bank offensive on May 10. But Israel's incursions and circling of Palestinian cities have prompted Yasser Arafat to threaten to delay long-sought reforms and elections within his own leadership.

The Palestinian leader demanded on Sunday that Israel "finish quickly the siege of all our cities and towns in the West Bank and Gaza" to facilitate preparations for an internationally supervised vote. Last week, Arafat promised legislative and presidential elections by next winter.