GAZA, Jul. 18 (Reuters) - Israeli forces bombarded the Gaza Strip's historic refugee camps in the centre of the enclave and struck Gaza City in the north on Thursday, killing at least 21 people, and tanks pushed deeper into Rafah in the south, health officials and residents said.

A barrage of Israeli airstrikes killed 16 in Zawayda town, Bureij and Nuseirat camps and the overcrowded city of Deir-Al-Balah, the last major urban centre in Gaza not to be invaded by Israeli forces, health officials said.

Prime Minister Benjamin Netanyahu, who is due to address the U.S. Congress next week, made a surprise visit to Israeli troops in the area around Rafah, telling them that military pressure combined with a demand to bring back 120 hostages still held in Gaza was producing results.

"This double pressure is not delaying the deal, it is advancing it," he said, according to a statement from his office.

The Israeli military said in a statement its forces killed two senior Islamic Jihad commanders in two airstrikes in Gaza City, including one whom it said had taken part in the Oct. 7 attack in southern Israel that triggered the Gaza war.

Palestinian medics said five people were killed in the two strikes.

In Rafah, residents said Israeli tanks advanced deeper in the western side of the city and took position on a hilltop there. The Israeli military said forces located several tunnels and killed several gunmen.

At Al-Amal Hospital, run by the Palestinian Red Crescent Society, in Khan Younis in southern Gaza, Palestinian health officials exhumed at least 12 bodies buried inside the medical facility to rebury them at another location.

Reuters journalists saw medical workers digging up bodies from graves inside the facility, wrapping them in white shrouds before placing them inside vehicles for transfer to a new burial site as some relatives watched, some in tears.

Areej Hamouda, a mother of one of the dead, clutched some of the sandy earth from the grave of her son and kissed it before medics exhumed the body.

"They (Israel) shot him and he had a loaf of bread with him, which he had to beg for to get for his daughter, they shot him in the eye and the head - it rained on him, he was washed with blood," Hamouda said, weeping.

"He was (lying) there all day long, they weren't able to move him, (then) they pulled him with a rope when they brought him to be buried here."

Photo from Reuters