Israel's operation against Hamas saw one of its bloodiest days on Saturday, with 47 Palestinians killed in Gaza and two Israeli soldiers and a civilian killed by militant fire.

As Israeli warplanes bombarded Gaza from the air, and ground troops pressed an assault on land, the Palestinian overall death toll on day 12 of Israel's Operation Protective Edge rose to 343, with rights groups warning that a growing number of victims were children.

UN chief Ban Ki-moon was Saturday headed for the region to bolster intense diplomatic efforts aimed at ending the bloodshed.

Despite the blistering Israeli offensive, Palestinian commandos in central Gaza managed to use tunnels to infiltrate southern Israel in three separate cases, killing two soldiers in one incident with four of their men dying in the attacks.

Also Saturday, an Israeli Bedouin was killed when a rocket hit his encampment in southern Israel in an attack which also wounded four of his family, among them two young children, police said.

The deaths raised to five the total number of Israelis killed since July 8 -- three soldiers and two civilians -- in the deadliest confrontation between Israel and Hamas militants since 2009.

According to army data, 76 rockets and mortars hit Israel on Saturday with another 14 intercepted, bringing the number of projectiles hitting Israel in the past 12 days to 1,321, with 356 intercepted.

One stray rocket probably fired from Gaza even hit Egypt's Rafah border crossing with the Strip, wounding a soldier, a security official said.

Child death toll

In Gaza, violence intensified with tank shelling and air strikes killing 47 people on Saturday.

Among the dead were two six-year-olds and a toddler, emergency services spokesman Ashraf al-Qudra said.

The increasing number of children killed in the conflict is causing a growing outcry, with a joint statement from NGOs War Child and Defence for Children International saying more children had been killed than militants.

Figures provided by the UN children's agency, UNICEF, indicate 73 of the victims were under the age of 18.

"Children should be protected from the violence, and they should not be the victims of a conflict for which they have no responsibility," UNICEF's Catherine Weibel told AFP.

Israel's Prime Minister Benjamin Netanyahu absolved Israel of all responsibility for civilian casualties, laying the blame squarely on the shoulders of Hamas.

A statement from Netanyahu's office cited him as telling Canadian Prime Minister Stephen Harper in a phone call that Hamas was "using innocent civilians as human shields for its terrorist activities; it is responsible if civilians are inadvertently hit."

The UN's Palestinian refugee agency, UNRWA, said earlier in the week it found 20 rockets stored in one of its schools in Gaza, condemning the "group or groups" involved.

UNRWA has opened 49 of its schools to shelter those fleeing the most heavily-bombarded areas.

So far, more than 60,000 Gazans have sought sanctuary at UN institutions, the agency said.

Ban was leaving for the Middle East on Saturday to help Israelis and Palestinians "end the violence and find a way forward", the UN said.

In Amman, French Foreign Minister Laurent Fabius said brokering a ceasefire must be the "absolute priority," urging all parties to accept an Egyptian-led effort.

Palestinian president Mahmud Abbas and Hamas political leader Khaled Meshaal will meanwhile meet in Qatar Sunday to discuss a truce in Gaza, an official close to Abbas said.

An Egyptian-led truce effort collapsed earlier this week after Israel accepted it but Hamas militants continued to fire rockets over the border.

Hamas spokesman Fawzi Barhum told AFP his movement had given "the demands of the resistance to all the parties concerned, including Qatar, Turkey and the Arab League" as well as Abbas and Egypt.

Popular unrest

The demands included an end of the "war on the Gaza Strip," a complete lift of the siege on it, opening the Rafah crossing with Egypt, freedom of movement in the border areas, cancelling the buffer zone and expanding the freedom to fish 12 nautical miles from shore.

In addition, Hamas demanded the release of its members who had been freed in the 2011 Shalit deal and recently re-arrested in an Israeli crackdown on the West Bank.

In northern Israel, the growing violence brought angry protesters onto the streets, where 1,500 Arab Israelis demonstrated in Kafr Kana against Israel's military operation, police said.

In the northern coastal city Haifa, some 800 Israelis held a demonstration in favour of Israel expanding its Gaza operation, while 350 Israelis at the same site were protesting against it.

Protests against the Israeli offensive have also sprung up across the world, with thousands joining a pro-Palestinian rally in London, chanting "Israel is a terror state", while demonstrators in Paris clashed with riot police after their own protest was banned.