GAZA CITY  - Israel declared a Gaza ceasefire over on Friday and killed 80 Palestinians in renewed shelling, as both sides accused each other of breaking the truce.

The Gaza Health Ministry said 80 people were killed and 220 wounded by Israeli shelling near the southern town of Rafah. The diplomats however still pressed for a more durable end to 25 days of devastating and highly disproportionate war.

The skies over Gaza initially fell silent after the humanitarian truce started at 0500 GMT, the latest and longest of several agreed since the conflict broke out on July 8.

It gave a brief respite to people in the battered strip, after more than three weeks of fighting that has killed 1,509 Palestinians – mostly civilians – and wounded 7,000. Israel says 63 of its soldiers and three civilians have been killed, and 400, mostly soldiers, injured.

The 72-hour break announced by US Secretary of State John Kerry and UN Secretary-General Ban Ki-moon was the most ambitious attempt so far to end more than three weeks of fighting, and followed mounting international alarm over a rising Palestinian civilian death toll.

The ceasefire was to be followed by Israeli-Palestinian negotiations in Cairo on a longer-term solution. Egyptian officials said the invitation still stood, but some Palestinian representatives had asked for a postponement until Saturday or Sunday to allow a new truce to be reached.

Israel alleged Hamas militants had breached the truce shortly after it began by killing two of its soldiers and apparently capturing another while they were searching for infiltration tunnels in Gaza.

Hamas for its part accused Israel of breaching the ceasefire after intensive shelling killed dozens of people in southern Gaza, but Washington sided with its ally's version of events.

Israeli military spokesman Lt-Col Peter Lerner alleged that 90 minutes into the truce, militants attacked soldiers searching for infiltration tunnels in the southern Gaza Strip.

Two of the soldiers were killed. "The initial indication suggests that a soldier has been abducted by terrorists during the incident," he said in a conference call with reporters.

There was no immediate word from militant groups on whether any were holding the soldier, identified by the military as Second Lieutenant Hadar Goldin, 23.

Sami Abu Zuhri, a spokesman for the dominant Hamas movement in Gaza, said Israel was trying to mislead the world and "cover up its Rafah massacre".

The truce had left Israeli ground forces in place in the Hamas-dominated Gaza Strip and a military spokeswoman had said operations would continue to destroy a warren of tunnels through which the Islamist group has menaced Israel's southern towns and army bases.

International calls for an end to the bloodshed intensified after shelling on Wednesday that killed 15 people sheltering in a UN-run school in Jabalya refugee camp. Hamas is seeking an end to Israel's blockade of Gaza and wants a hostile Egypt to ease restrictions at its Rafah crossing with the territory.