The moves came after thousands of troops moved into southern Gaza Wednesday and Israeli warplanes roared over the summer home of Syria's president, who is blamed for harboring Hamas leaders.
Palestinian witnesses said Israeli tanks and bulldozers entered northern Gaza before daybreak Thursday, adding a second front to the Israeli action in Gaza. The Israeli military had no comment on the latest incursion.
Adding to the tension, a Palestinian militant group said it killed an 18-year-old Jewish settler kidnapped in the West Bank. Palestinian security officials said they believed the body of Eliahu Asheri had been found in the West Bank city of Ramallah.
No deaths or injuries were reported in the Israeli actions so far. But the warplanes knocked out Gaza's electric power plant, raising the specter of a humanitarian crisis. The Hamas-led government warned of "epidemics and health disasters" because of damaged water pipes to central Gaza and the lack of power to pump water.
Gaza City is one of the most densely populated cities on the planet and hundreds of thousands of people are living in the dark, reports CBS News correspondent Sheila MacVicar.
Increasing pressure on Hamas within the Palestinian territories, Israeli forces arrested more than 30 lawmakers, according to Palestinian security officials. Among those detained were Palestinian Deputy Prime Minister Nasser Shaer, Labor Minister Mohammed Barghouti and two other ministers in the West Bank. They security officials said two others were arrested in the town of Jenin, and Israeli media reported a roundup of Hamas lawmakers in Jerusalem and other locations.
Although the Israeli action was sparked by the abduction of the soldier, Israeli Prime Minister Ehud Olmert's government also is alarmed by the firing of homemade rockets on Israeli communities around Gaza and support for Hamas in the Arab world, especially from Syria.
In a clear warning to Syrian President Bashar Assad, Israeli airplanes flew over his seaside home near the Mediterranean port city of Latakia in northwestern Syria, military officials confirmed, citing the "direct link" between his government and Hamas. Israeli television reports said four planes were involved in the low-altitude flight, and that Assad was there at the time.
Syria confirmed Israeli warplanes entered its airspace, but said its air defenses forced the Israeli aircraft to flee.
As CBS 60 Minutes correspondent Bob Simon reports, the violence is part of the typical pattern of Middle East violence. Simon reports that the kidnapping "is designed to provoke a brutal Israeli response. The Israeli's follow suit with that response. The response invariably radicalizes the population, makes them even more anti-Israeli – creates mores suicide bombers."
In Gaza late Wednesday, Israeli missiles also hit two empty Hamas training camps, a rocket-building factory and several roads. Warplanes flew low over the coastal strip, rocking it with sonic booms and shattering windows. Troops in Israel backed up the assault with artillery fire.
The area's normally bustling streets were eerily deserted, with people taking refuge inside their homes.
Witnesses reported heavy shelling around Gaza's long-closed airport, which Israeli troops took over. Dozens of people living near the airport fled to nearby Rafah.
In Rafah, Nivine Abu Shbeke, a 23-year-old mother of three, hoarded bags of flour, boxes of vegetables and other supplies. "We're worried about how long the food will last," she said. "The children devour everything."
Prior to the latest incursion into northern Gaza, the Israeli army dropped leaflets warning residents of impending military activity.
Dozens of Palestinian militants — armed with automatic weapons and grenades — took up positions, bracing for the attack.
Anxious Palestinians pondered whether the incursion, the first large-scale ground offensive since Israel withdrew from Gaza last year, was essentially a "shock and awe" display designed to intimidate militants, or the prelude to a full-scale invasion.
Olmert threatened harsher action, though he said there was no plan to reoccupy Gaza. Palestinian President Mahmoud Abbas deplored the incursion as a "crime against humanity."
The Israeli assault came as diplomatic efforts to free the 19-year-old Israeli soldier, Cpl. Gilad Shalit, bogged down with Hamas demanding a prisoner swap and Israel refusing, demanding Shalit's unconditional release. Shalit was abducted by Hamas-linked militants on Sunday and is believed to be in southern Gaza.
"We won't hesitate to carry out extreme action to bring Gilad back to his family," Olmert declared.