Israel is on high alert for possible Palestinian attacks, as the country stops to commemorate Yom Kippur, the holiest day in the Jewish calendar.
Israel has sealed off the West Bank and Gaza Strip for Yom Kippur, the Day of Atonement, which begins Sunday night. The holy day ends at sunset on Monday, but the closure of the territories will remain in effect until Tuesday morning.
Palestinian businessmen and those normally allowed into Israel will not be permitted to enter the Jewish State. Crossing points at the Egyptian and Jordanian borders will also be closed.
Curfews remain in place on most Palestinian cities.
Israeli army radio says there are also warnings that Palestinian militants will attempt to infiltrate Jewish settlements in the West Bank and Gaza Strip.
On the eve of Yom Kippur, an Israeli air force helicopter came under attack from Palestinian gunfire near the West Bank city of Tulkarem. The pilot brought down the machine safely, and there were no reports of injuries to the crew.
Tulkarem is one of the cities placed under Israeli military control since June, following a series of Palestinian suicide bombings.
Palestinian officials say Israeli troops Sunday also entered three Palestinian self-rule areas of the Gaza Strip.
According to the officials, Israeli tanks were seen on the outskirts of Gaza City, and some had entered two kilometers into the city.
Palestinian officials claim that Israeli troops also entered Beit Lahiya, in the southern Gaza Strip, and were operating between Khan Younis and Rafah, on the border with Egypt.
An Israeli army spokesman says the incursions are part of a crackdown on Palestinian militants.