"The Israeli army assassinated Hamas political bureau member Ismail Barhoum," the Hamas source said, requesting anonymity to speak more freely.

"Warplanes bombed the operating room at Nasser Hospital in Khan Yunis, where Barhoum was receiving treatment after sustaining critical injuries in an air strike targeting his home in Khan Yunis at dawn last Tuesday."

AFP photos showed the building of about four-storeys largely undamaged except for fire blazing in one section off a stairwell.

Barhoum is the fourth member of Hamas's political bureau killed since last Tuesday when Israel resumed air strikes in the territory after an impasse over continuing a ceasefire.

Israel's military confirmed the hospital strike which it said was conducted with "precise munitions" following extensive intelligence-gathering.

It said in a statement that the target was a key member of "the Hamas terrorist organisation who was operating inside the Nasser Hospital compound," the military said.

The Ministry of Health in Hamas-run Gaza said Israeli forces "have just targeted the surgery building inside the Nasser Medical Complex, which houses many patients and wounded individuals, and a large fire has erupted at the site."

Gaza's civil defence rescue agency said the hospital's emergency department had been targeted. The agency did not provide immediate details on casualties.

Earlier Sunday, Hamas said an Israeli air strike the previous day near Khan Yunis killed Salah al-Bardawil, a senior member of its political bureau.

Bardawil, 65, was killed along with his wife in a camp in al-Mawasi, the group said.

The Israeli military confirmed that it had targeted Bardawil, saying that "as part of his role, (he) directed the strategic and military planning" of Hamas in Gaza.

His "elimination further degrades Hamas' military and government capabilities", it added.