GAZA CITY: A three-day Gaza ceasefire that began Friday quickly unraveled, with Israel and Hamas accusing each other of violating the truce as four Palestinians were killed in a heavy exchange of fire in the southern town of Rafah.

The ceasefire, announced by the US and the UN hours earlier, took effect at 8:00 a.m. Friday after heavy fighting that killed 17 Palestinians and five Israeli soldiers.

Israel and Hamas agreed to halt all aggressive operations and conduct only defensive missions. But US Secretary of State John Kerry cautioned there were “no guarantees” that the lull would bring an end to the war, now in its fourth week.

Nearly two hours after the ceasefire went into effect, Israeli tanks shelled the eastern part of Rafah, which lies close to Gaza's borders with Israel and Egypt, killing at least four people and wounding 15, said Health Ministry official Ashraf al-Kidra and Gaza police spokesman Ayman Batniji.

An Israeli Army spokesman said a heavy exchange of fire had erupted in the Rafah area, without providing further details.

“Once again, Hamas and the terror organisations in Gaza have blatantly broken the ceasefire to which they committed, this time before the American Secretary of State and the UN Secretary General,” Israeli Prime Minister Benjamin Netanyahu's office said in a statement.

Israel launched an aerial campaign against Gaza aimed at halting Palestinian rocket fire on July 8 and later sent in ground troops to target launch sites and tunnels used by Hamas to carry out attacks inside Israel. The war has killed more than 1,450 Palestinians, mainly civilians, and more than 60 Israelis, nearly all soldiers.

At least four short humanitarian ceasefires have been announced since the conflict began, but each has been broken within a few hours by renewed fighting. Friday's temporary ceasefire was the longest to be announced thus far. Under the ceasefire, Israeli troops on the ground in Gaza can continue to destroy tunnels along the heavily guarded frontier, but only those that are behind Israeli defensive lines and lead into Israel.

Netanyahu on Thursday vowed to destroy Hamas' tunnel network “with or without a ceasefire”. But military spokesman Moti Almoz told Army Radio on Friday that Israel would not be able to eliminate the tunnel threat “100 per cent“.

Soon after the ceasefire went into force, Gaza's residents took advantage of the truce to return to their homes, many of which had been destroyed in the fighting. Some arrived on tuk-tuks — three-wheeled taxis — by car or on foot to retrieve their belongings.

Near a main road in the heavily bombarded Gaza district of Shijaiyah, less than a mile from the Israeli border, residents surveyed extensive damage. Basem Abul Qumbus returned to find his three-story home — in which he had invested tens of thousands of dollars — uninhabitable.

Tank shells had punched a hole in the ceiling of one bedroom and a wall had collapsed into the kitchen. “The work of all those years is gone,” he said, as he struggled to salvage flour from bags that had been torn apart by shrapnel.

Food supplies are running short in the blockaded coastal territory in the war's fourth week. Egypt issued a statement early Friday calling on the Western-backed Palestinian Authority and Israel to send negotiation teams to Cairo to discuss “all issues of concern to each party within the framework of the Egyptian initiative“.

Egypt had put forth a ceasefire proposal a week after fighting began last month. Israel accepted the proposal, but Hamas, which deeply mistrusts Egypt following last summer's overthrow of the Muslim Brotherhood government in Cairo, rejected it.

Hamas has demanded the lifting of an Israeli and Egyptian border blockade imposed on Gaza in 2007 when the group seized power, as well as the release of Palestinians rounded up in the West Bank in June following the killing of three Israeli teenagers.

In recent weeks Turkey and Qatar, which have warmer ties to Hamas but are at odds with Egypt, have tried to help broker a ceasefire agreement, with no results. It's not clear whether other nations will attend the Egypt talks, and aides to Kerry said Egypt will ultimately decide who will participate. A Hamas official in Qatar said Hamas and Islamic Jihad officials would be participating. Israel will not meet directly with members of either group because it considers them terrorist organisations.

Hours before the ceasefire was to take effect, 17 Palestinians were killed in Israeli strikes, including 10 from the same family, according to al-Kidra, the Health Ministry official in Gaza. He said the family members were killed in an airstrike on their home in the southern Gaza town of Khan Younis.

Israel's military said five of its soldiers were killed along the Gaza border Thursday evening by a mortar round. More than 1,450 Palestinians, mainly civilians, have been killed since hostilities began July 8, according to Palestinian officials. Israel says 61 of its soldiers and three civilians in Israel have been killed.

Hours ahead of the ceasefire, Gaza police reported heavy Israeli tank shelling in northern and eastern Gaza, and the loud exchange of fire with militants could be heard across Gaza City. Tank shells slammed into the city itself, setting homes and shops ablaze. Hamas fighters hit an Israeli tank with an anti-tank missile, Gaza police said.

The militants then attacked Israeli troops who came to evacuate the tank crew. Clashes continued into the early morning hours, police said.

The Israeli military said it was looking into the matter. Israeli police meanwhile warned residents to stay away from Israeli communities near the Gaza border during the ceasefire, saying the area remains “a war zone“.

“We ask the public to heed the orders of the police and army and not to go to the Gaza Strip border area, it is a threat to your life!!!” the police said in a statement.

Police said Palestinians clashed with Israeli security forces in a number of neighbourhoods in east Jerusalem, and that Israelis attacked an empty bus. Police also restricted the entry of worshippers to a key Muslim holy site in the city to prevent disturbances.