Israeli tanks and bulldozers dug in across a mile-wide strip of Gaza’s eastern frontier on Saturday, as Palestinian officials said military strikes had killed more than 300 people, most of them civilians.

Israel sent in ground forces late on Thursday after 10 days of air and naval barrages failed to stop rocket fire from Gaza.

The military said its engineers were concentrating on a buffer zone 2.5 km (1.5 mile) wide and were looking to destroy concealed rocket launch pads and tunnels dug by Gaza’s dominant Hamas Islamists after the last big flare-up of violence in 2012.

Military spokesman Lieutenant-Colonel Peter Lerner said 13 tunnels, at least one of them 30 metres (90 feet) deep, and 95 rocket launchers were found and destroyed in the Gaza sweep.

Searches were continuing in what he described as an open-ended mission that had “severely impeded Hamas capabilities”.

FRANCE 24’s Israel correspondent Irris Makler, reporting from Jerusalem, said that: “The Israeli army says these tunnels are very well-constructed with concrete and electricity… like a bomb-making factory under the ground.”

“The Israeli boots in Gaza remain in a perimeter area, searching out these tunnels,” she added. “They haven’t gone far into Gaza. If they expand this operation, it will mean going farther into the Gaza Strip, going to Hamas and Islamic jihad rocket launching sites, which is fraught with danger.”

Hamas said its fighters used one such tunnel to slip into Israel on Saturday, inflicting casualties. The Israeli military confirmed the incident near central Gaza, saying it killed one militant, repelled the rest, and four soldiers were wounded.

Gaza on ‘the verge of critical humanitarian situation’

Palestinians also launched at least 18 rockets into Israel on Saturday, killing a man and wounding four people, including two children, in a southern Bedouin Arab village, police said.

Gaza officials said that at least 325 Palestinians, including 70 children, have been killed in the 12-day conflict.

On Israel’s side, a soldier and two civilians have died.

Hostilities had escalated following the killing last month of three Jewish seminary students that Israel blames on Hamas. Hamas neither confirmed nor denied involvement. The apparent revenge murder of a Palestinian youth in Jerusalem, for which Israel has charged three Jews, further fuelled tensions.

FRANCE 24’s Gallagher Fenwick, reporting from Gaza City, said “The north is being pounded, there is very little time between hits, it is very frightening.”

“The scenes of destruction are all over,” he added. “When these apartments get hit by Israeli projectiles, the explosion is so hard that it sends everything flying through the air and you find family’s entire personal effects strewn in the street.”

The United Nations said more than 50,000 Palestinians had taken refuge from Israeli attacks in its various Gaza buildings.

“The UN says that the situation is alarming,” Fenwick reported. “They are hosting tens of thousands of Palestinians and they say about 900,000 have no running water. Gaza is on the verge of a critical humanitarian situation”.

Palestinian officials said 90 percent of Gaza’s electricity had been cut by Israel. The Israeli energy ministry had no immediate response. On Sunday, it said a Palestinian rocket had crippled a power line to Gaza from Israel and it would not endanger engineers by sending them to conduct repairs.

Israel says it tries to avoid civilian casualties and that Hamas invites them by operating from within urban areas.

No ceasefire

The escalation of hostilities, and its toll on Gaza’s 1.8 million Palestinians as well as on Israelis jarred by rockets that have reached Tel Aviv and beyond, have spurred so-far fruitless truce bids by Western powers and regional go-betweens.

Egypt has no plans to revise its ceasefire proposal, which Hamas has rejected, Cairo’s foreign minister said on Saturday.

UN Secretary-General Ban Ki-moon planned to travel to Israel and the Palestinian territories this weekend. Palestinian President Mahmoud Abbas is also looking to secure a ceasefire and was due to travel to regional power Qatar later in the day to see the emir of the Gulf state. It was not clear whether he would also see Hamas’s leader, Khaled Meshaal, who lives in exile in Qatar.

France has also mooted mediation by Qatar, which has helped fund Gaza projects in the past, but Israel is cool to the idea.

The Israelis prefer Egyptian intercession. Yet with Egypt having cracked down on its Muslim Brotherhood - Hamas’s ideological kind - and viewing Hamas as a security threat, Cairo’s clout with the Palestinian Islamists is in doubt.

“There will be no truce without an end to the war that the Occupation (Israel) began, a lifting of the blockade and a halt to all violations and killings in Gaza and the West Bank,” Hamas spokesman Sami Abu Zuhri said in Gaza.

Hamas, Gaza’s dominant Islamist group, refuses to hold fire unless embargoes by Israel and neighbouring Egypt are eased and other demands are met. The Israelis say they are ready to step up their Gaza assault, though they do not aim to topple Hamas.

(FRANCE 24 with REUTERS)