Jan. 4 (Bloomberg) -- Israeli forces moved into the Gaza Strip, broadening an offensive against Hamas aimed at forcing the Islamist Palestinian group to stop firing rockets at the Jewish state’s southern cities.

“A few hours ago Israeli forces went into Gaza as part of the ongoing operation there. From the beginning, I said that the operation would be broadened as necessary, and now it is necessary,” Israeli Defense Minister Ehud Barak said last night in a televised press conference from Tel Aviv.

Infantry, tanks, engineering forces, artillery and intelligence units are taking part in the ground offensive, backed by the air force, navy and other security agencies, the army said. A naval blockade was imposed at 20 nautical miles off the Gaza shore, it added.

The ground offensive is likely to increase casualties on both sides, with Israel running the risk of finding itself in a quagmire with no easy exit strategy and facing increased international pressure to call a cease-fire. The operation comes after Foreign Minister Tzipi Livni said on Channel Two that Israel was “determined” to meet the goals of the operation against Hamas.

“The objective of this phase of the operation is to intensify the heavy blow already dealt to Hamas and to take control of area from where most of the rocket attacks against Israel originate,” Israel Army spokesman Brigadier-General Avi Benayahu said in an e-mailed statement.

Obama ‘Monitoring’

In Washington, the White House said that President George W. Bush was briefed on the Israeli military’s actions, and that U.S. officials had been in regular contact with the Israelis, and regional and European officials. President-elect Barack Obama “is closely monitoring global events, including the situation in Gaza,” Brooke Anderson, his chief national security spokeswoman, said in a statement. Israel notified Joint Chiefs Chairman Mike Mullen before it launched the ground attack, CNN said.

On a road that runs parallel to the eastern border fence of the Gaza Strip, artillery rounds were heard every 20 seconds, and flashes of light were seen in the sky from the air strikes. Hundreds of tanks, armored personnel carriers and other military vehicles were holding their position on fields between the road and the Gaza frontier, awaiting orders to proceed.

Palestinian gunmen clashed with Israeli troops inside Gaza and more than 30 Hamas militants were killed in the battle, Channel Two television said, citing the army. An army spokeswoman declined to comment.

‘High Price’

Hamas’s armed wing said that Israel will pay a “high price” for its ground offensive in the Gaza Strip. “The Zionist enemy is getting very close to the trap we have prepared for them,” the group said in a message sent to journalists by text message.

“We will fight till our last breath, your invasion of Gaza will not be a cake walk, Gaza will be your cemetery and you have no choice but to end the aggression and lift the blockade,” Hamas spokesman Ismail Radwan said in a statement broadcast on Qatar’s Al-Jazeera television.

Hamas said it planned to send suicide bombers to Israeli cities and kidnap more Israeli soldiers. Corporal Gilad Shalit has been held captive in Gaza for more than two years.

The ground invasion will prevent rocket attacks from certain areas, isolate Gaza from Egypt, and give the army an opportunity to arrest Hamas figures who could then be used as bargaining chips to free Shalit, said former deputy chief of staff Uzi Dayan.

‘Pressure Them’

It also will allow the military to seize parts of Gaza that could be later exchanged as part of a new cease-fire agreement while at the same time enable Israel “to more effectively go after the Hamas leadership and pressure them,” he said by phone.

“Whatever the short-term goals, I believe we have to aim not just for a halt to rocket fire, but to topple the Hamas regime in Gaza completely, or any of the gains will be temporary,” he added.

The Israeli government cleared the way yesterday for the call-up of tens of thousands of reservists, expanding an earlier approval for the drafting of 7,000 soldiers in the reserves, according to a statement on Prime Minister Ehud Olmert’s Web site.

The army said that it issued “many” draft notices to reserve soldiers in combat units.

“This will not be easy. It will not be short,” Barak said. He warned the Shiite Muslim Hezbollah in south Lebanon, with which Israel fought a monthlong war in 2006, that Israel would retaliate if fired on.

Northern Border

“We are also watching the northern border. We hope that the northern border will stay quiet but we are ready and prepared for any possibility,” he said.

Hezbollah leader Sheik Hassan Nasrallah urged Hamas to inflict maximum losses on the Israeli forces in remarks to the militia’s Al-Manar television.

Israel began the campaign to halt rocket attacks by Islamic militants after a six-month cease-fire with Hamas expired Dec. 19. Militants launched more than 3,000 rockets and mortar shells at Israel since the beginning of 2008, the Israeli army said. Hamas refused to renew the cease-fire because it said Israel had not eased its economic blockade of Gaza and launched 70 rockets at Israel the day before it ended.

More than 435 Palestinians have been killed and 2,285 wounded since Israel started its aerial campaign on Dec. 27, according to the Palestinian Authority’s emergency services office in Gaza City. Four Israelis have died in the violence.

‘Mistake’

The Israeli government rejected Dec. 31 a French proposal for a temporary cease-fire with Hamas, saying it would be a “mistake” to give the movement time to rearm and regroup.

Hamas denies Israel’s right to exist and condemns Palestinian Authority President Mahmoud Abbas as a stooge for conducting peace talks over the past year. Hamas seized control of Gaza in 2007 after a brief power-sharing arrangement with Abbas, of the rival Fatah movement. The Palestinian Authority said it was halting peace talks because of Israel’s offensive.

The strikes on Gaza, where about 1.4 million people live on a strip that is about 40 kilometers long and 25 kilometers across, have triggered global calls for restraint.

A delegation from the European Union, led by Czech Foreign Minister Karel Schwarzenberg, planned to come to Israel on Jan. 6 to seek a truce. French President Nicolas Sarkozy also plans a Middle East tour.

In London, a Downing Street spokesman said before Israel launched the ground initiative that Prime Minister Gordon Brown was “pressing hard for an immediate cease-fire. Rocket attacks from Hamas must stop, and we have called for a halt to Israeli military action in Gaza.”

To contact the reporters on this story: Gwen Ackerman in Jerusalem at gackermanbloomberg.net; Saud Abu Ramadan in Gaza City through the Tel Aviv newsroomt .

Last Updated: January 3, 2009 17:08 EST