A 24-hour ceasefire announced by Hamas in Gaza appears to be stalling, with both Palestinian militants and Israel continuing their offensives.
Hamas fired more rockets into Israel, accusing it of failing to abide by the ceasefire.
Israel rejected the truce, PM Benjamin Netanyahu saying: "Israel will do what it must do to defend its people".
More than 1,030 Palestinians, mostly civilians, and 43 Israeli soldiers and two Israeli civilians have been killed.
A Thai national in Israel has also died. The Gaza health ministry on Sunday revised the number of dead down by 30 after some relatives found missing family members.
The latest developments further undermined hopes that Saturday's humanitarian truce observed by both sides could be extended, although Israeli TV reported on Sunday that an "understanding on holding fire" had been reached between Israel and Hamas, whereby "quiet will be met with quiet".
However, President Barack Obama phoned Mr Netanyahu on Sunday to urge "an immediate, unconditional humanitarian ceasefire that ends hostilities now".
He added that a long-term solution would have to allow "Palestinians in Gaza to lead normal lives" and "must ensure the disarmament of terrorist groups and the demilitarisation of Gaza".
A 12-hour pause on Saturday enabled Gaza residents to gather supplies and retrieve bodies buried under the rubble.
Israel later accepted a UN-requested 24-hour ceasefire until the end of Sunday, although it said ground forces would continue to destroy tunnels used by Hamas.
However, the Israeli military announced on Sunday morning it had decided to resume its air, ground and naval raids on Gaza in response to "incessant rocket fire" from Hamas, which has controlled Gaza since seizing power there in 2007.
Shortly after Israeli raids resumed, Hamas said it had decided to agree to a humanitarian truce, starting at 14:00 local time (11:00 GMT).
Weekend ceasefires timeline
- Saturday 26 July: 12-hour humanitarian truce observed by both sides from 05:00 GMT (08:00 local time) till 17:00 GMT
- Israeli cabinet agrees four-hour extension until 21:00 GMT while it considers UN request for 24-hour extension, but continues operation against "terrorist" tunnels
- Hamas rejects extension to 21:00 GMT because it wants "complete" stop to fighting and end to Gaza blockade
- Israel announces extension of ceasefire for 24 hours till 21:00 GMT on Sunday
- Sunday 27 July: Israel resumes operation in response to "incessant rocket fire" from Gaza
- Hamas declares 24-hour truce, but continues rocket fire. Israel rejects ceasefire
The pause was "as a preparation for the end of (the Islamic holy month of) Ramadan and in response to the UN mediation and also regarding our people's living circumstances".
But in an interview with CNN, Mr Netanyahu said: "Hamas doesn't even accept its own ceasefire. It's continuing to fire at us as we speak".
Israel launched its military offensive on 8 July with the declared objective of stopping Hamas firing rockets from Gaza into Israel.
On 18 July, it extended operations with a ground offensive, saying it was necessary to destroy tunnels dug by militants to infiltrate Israel.
Correspondents in Gaza said loud explosions could be heard in several districts as Israeli forces resumed their air strikes. Palestinian eyewitnesses reported heavy shelling to the east of Gaza City.
At least eight Palestinians have died in Sunday's attacks, according to Gazan health officials.
Dozens of Hamas rockets were fired into Israel on Sunday, with some intercepted by Israel's Iron Dome missile shield, according to the Israel Defense Forces (IDF).
The IDF added that a soldier was killed by a mortar bomb fired from Gaza early on Sunday morning.
Also on Sunday, the Israeli army admitted it fired a mortar round into the courtyard of a UN shelter in Gaza on Thursday in a clash with "militants", but denied it was responsible for the deaths of at least 15 people.
Despite rising concern about military casualties, support in Israel for the offensive remains widespread, the BBC's Bethany Bell reports from Jerusalem, as people see the country as being under attack.
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