GAZA CITY (AFP) - The death toll from Israel's ongoing air campaign against Gaza militants rose to 176 on Monday, as a UN official said over a quarter of the victims were children.

In the latest strikes, a 37-year-old was killed when a missile struck a group of men near the southern city of Khan Yunis, emergency services spokesman Ashraf al-Qudra said.

A 60-year-old man was killed in a raid on a house in Deir al-Balah in central Gaza, and two other people died in separate strikes elsewhere in the coastal enclave, Qudra said, without giving details.

Earlier, a man and a woman injured in air strikes on Sunday died of their injuries, he said, raising to six the number of lives lost on Monday as a result of the ongoing air campaign.

So far, more than 1,280 have been wounded.

The Gaza-based Palestinian Centre for Human Rights said on Sunday that more than three-quarters of the victims were civilians.

The UN refugee for Palestinian refugees (UNRWA) has said more than a quarter of them were children.

"All indications are, and I find this particularly dramatic, that women and children make up a sizable number of the victims of the current strikes. Currently more than one quarter of the fatalities are children," UNRWA Commissioner-General Pierre Krahenbuhl said on Monday.

The bloodiest day so far was Saturday when 56 people were killed in a series of deadly strikes, Qudra said.

No Israelis have been killed, although three people in the Jewish state have been seriously wounded since the start of the operation, medics said.

Israel began Operation Protective Edge before dawn on Tuesday in an attempt to halt cross-border rocket fire by militant groups.

Since then, more than 800 rockets have hit Israel, while some 187 others have been intercepted by its Iron Dome air defence system, the army said.

Of that number, 55 rockets struck Israel on Sunday with another 12 shot down, a spokesman said.