Israeli soldiers entered the northern Gaza Strip at dawn on Monday for the first time since a teenage serviceman was abducted by Palestinian militants eight days ago.
"A limited number of troops entered the northern Gaza Strip to conduct searches for explosive devices and tunnels" dug by militants into Israel, a military source said.
The action came a day after Hamas militants threatened to attack civilians in Israel if Israel does not end its offensive on the Gaza Strip, launched in a bid to secure the release of 19-year-old Gilad Shalit.
Around 25 Israeli tanks crossed the border, said a witness on the northern Gaza border.
The military source confirmed that tanks and armoured vehicles had entered the area, but insisted the operation was to remain limited in scope and duration.
Prime Minister Ehud Olmert last Thursday delayed plans to send troops into the northern Gaza town of Beit Hanun, an operation intended to end Palestinian rocket attacks on Israel but likely to incur heavy casualties.
Israel's operation began last week, moving ground troops into areas around Rafah in southern Gaza where the soldier, who was abducted in a deadly Palestinian raid on an Israeli border post on June 25, is believed to be held.
Aircraft have also carried out six consecutive nights of aerial attacks, striking at the heart of the Hamas-led Palestinian government in a bid to tighten the pressure on the leadership to secure the soldier's release.
About 5,000 troops and columns of Israeli tanks are poised on the Gaza border in the largest Israeli military operation since it pulled out of the tiny coastal territory last September, ending a 38-year occupation.
Nineteen-year-old Corporal Gilad Shalit was snatched in a Palestinian raid in which two other servicemen were killed, an attack claimed by three militant groups, including the armed wing of Hamas.