By Nidal al-Mughrabi
GAZA (Reuters) - Israeli tanks and infantry battled Hamas fighters in the Gaza Strip on Sunday in a ground offensive launched after eight days of deadly air strikes failed to halt the Islamist group's rocket attacks on Israel.
Wearing night-vision goggles on their helmets and camouflage paint on their faces, Israeli soldiers entered the densely populated enclave on Saturday along with tank columns that swept in from four points as combat helicopters flew overhead.
In initial fighting, Israeli ground forces killed eight Gazans, five of them gunmen, bringing the Palestinian death toll since the start of an air campaign on December 27 to more than 450, medical officials said.
There was no official word of any Israeli casualties.
Israel said it called up tens of thousands of reservists and the military's chief spokesman estimated the operation in the Hamas-run territory could take "many long days."
Heavy casualties are likely to increase international pressure on Israel to halt its biggest operation in the Gaza Strip in four decades, fighting that holds significant political risks for Israeli leaders ahead of a February 10 national election.
The plight of the 1.5 million Palestinians crammed into the Gaza Strip was growing more desperate. People have taken shelter in their homes for days and humanitarian agencies warned that water, food and medical supplies were running short.
Several hours into the armoured offensive, Israeli forces had taken up positions in the northern Gaza Strip, in an area frequently used by militants to fire rockets across the border and near the southern town of Rafah, witnesses said.
A spokesman for Hamas's armed wing, the Izz el-Deen al-Qassam Brigades, said Israeli troops faced certain death or capture. "The Zionist enemy must know his battle in Gaza is a losing one," said the spokesman, Abu Ubaida.
At least a quarter of the 453 Palestinians killed in the current conflict have been civilians, a U.N. agency said. Another 2,050 Palestinians have been wounded. A leading Palestinian rights group put the number at 40 percent.
Four Israelis have been killed by rockets that continue to pound southern Israel, where residents have been told to stay home and take cover in rooms made of reinforced concrete. Israel carried out more air strikes in the Gaza Strip on Sunday.
The U.N. Security Council convened for a special meeting to discuss the latest developments. Council diplomats said it would debate a Libyan-drafted statement that would have them express "serious concern at the escalation of the situation in Gaza, in particular after the launching of the Israeli ground offensive."
It also called on all parties to "to observe an immediate cease-fire" and to "stop immediately all military activities." The Libyan draft would need the support of all 15 council members to pass. It was not clear if the United States would back the text in its current form.
The U.S. State Department said a cease-fire should take place "as soon as possible," in a statement that urged Israel to be "mindful of the potential consequences to civilians" but did not refer directly to the invasion or call for an immediate truce.
Washington, the statement said, was working towards a cease-fire that would not allow for a re-establishment of the status quo, "where Hamas can continue to launch rockets out of Gaza and to condemn the people of Gaza to a life of misery."
A spokesman for Palestinian President Mahmoud Abbas condemned the Israeli attack as "a vicious aggression."
Israeli Defence Minister Ehud Barak said the aim of the ground push was to "protect the home front" from rocket attacks. He refrained in a televised address from making any threat to try to topple the Hamas government in the enclave.
"It won't be easy. It won't be short," said Barak, leader of the centre-left Labour party and a candidate for prime minister in an election that opinion polls predict will return right-winger Benjamin Netanyahu to power.
Large numbers of forces were involved in the sweep, including infantry, tanks, engineers, artillery and intelligence, the military said in a statement.
"The objective is to destroy the Hamas terror infrastructure in the area of operations," Major Avital Leibovich said. Israeli military affairs commentators said the offensive was also aimed at boosting Israel's deterrence power in the region.
Israeli troops face Hamas fighters whom the United States and Israel say have received arms and training from Iran. Hamas is believed to have about 25,000 fighters and has placed landmines and other traps in anticipation of an invasion.
An Egyptian-brokered six-month truce expired on December 19 but it had been strained by Hamas rocket strikes and Israeli military operations against the group.
Former British Prime Minister Tony Blair, representing major powers sponsoring Middle East peace talks, planned to begin shuttling on Sunday between Israeli leaders and Palestinian leaders -- Hamas's rivals -- in the occupied West Bank.
But divisions within the European Union over the Israeli operation could buy Israel more time.
France condemned the Israeli ground assault, as well as Hamas rocket fire. On Monday, French President Nicolas Sarkozy is scheduled to go to Jerusalem. Israel had rejected Paris's calls for a 48-hour cease-fire.
Diplomats said the Europeans were drafting a new proposal for a truce. Political sources said some Israeli officials favour a formal cease-fire backed by the U.N. and major powers. Other decision makers in Israel say it would only tie their hands should rocket fire continue.
Before the advance, an air strike killed 11 Palestinian worshippers, including children, and wounded dozens at a mosque in northern Gaza, Hamas officials and medics said. Israel says Hamas has used mosques as command posts and fire bases.
Israel's attacks brought a wave of international protests and thousands of demonstrators marched in solidarity with the Palestinians in European cities on Saturday.
(Writing by Jeffrey Heller and Adam Entous; Additional reporting by Dan Williams; Editing by Matthew Jones)