Israeli troops fought militants across Gaza on Wednesday, including in the southern city of Rafah which had been a refuge for civilians, in an upsurge of the more than seven-month war that has killed tens of thousands of Palestinians.

Antagonism between Israel and the UN worsened as the Israeli army sought an explanation for footage showing armed men next to UN Palestinian relief agency vehicles. Separately, the UN said it was investigating an unidentified strike that killed an international staffer in Gaza earlier this week.

Prime Minister Benjamin Netanyahu's army has in recent days pressed into the east of Rafah in pursuit of what it says are four Hamas battalions, despite warnings from its ally the US and others to hold off to avoid mass civilian casualties.

Since Hamas' October 7 attack, Israel has killed 35,000 Palestinians, according to Gaza health officials, with 82 dead on Tuesday in the highest single-day toll for weeks.

Hamas-led gunmen killed some 1,200 people in their initial raid, according to Israeli tallies, and still hold 128 hostages out of 252 they captured in their cross-border raid.

In the northern Jabalia refugee camp, residents said Israeli tanks had destroyed clusters of homes but were facing heavy resistance. "They are bombing houses on top of their inhabitants. We know of many families being trapped inside their homes," said Abu Jehad.

Hamas ally Islamic Jihad said it killed some foot soldiers in Jabalia, while Israel's military said it had eliminated "a large number of terrorists" in the camp, which it had claimed to have cleared months ago.

In Rafah, where more than 1 million of Gaza's 2.3 million people had fled from fighting elsewhere, residents said Palestinian gunmen were trying to prevent Israeli soldiers and tanks pushing towards the centre.

Israel said its troops targeted a training compound in the city's east, killing militants in close-quarters combat and finding large amounts of weapons.

Israel reported one death in south Gaza which public broadcaster Kan said was the first such fatality since the start of a ground operation there last week. Over the past day, aircraft hit about 80 militant targets, Israel's military said.

Israel said its troops had identified fighters in the central logistics compound of the UN Palestinian relief agency UNRWA east of Rafah, demanding an explanation. Reuters verified the location of the footage released by the Israeli army but could not verify when it was filmed or the identity of the men.

UNRWA said it was examining the footage and would share information when possible. Senior Hamas official Sami Abu Zuhri told Reuters the men were there to protect aid distribution.