(Refiles to fix typo 'says' in headline)

By Nidal al-Mughrabi and Alexander Cornwell

CAIRO/TEL AVIV (Reuters) -Israel has stopped aid from entering northern Gaza but is still allowing it to enter from the south, two officials said on Thursday after images circulated of masked men on aid trucks who clan leaders said were protecting aid, not Hamas stealing it.

Israeli Prime Minister Benjamin Netanyahu, in a joint statement with Defense Minister Israel Katz, said late on Wednesday that he had ordered the military to present a plan within two days to prevent Hamas from taking control of aid.

They cited new unspecified information indicating that Hamas was seizing aid intended for civilians in northern Gaza. A video circulating on Wednesday showed dozens of masked men, some armed with rifles but most carrying sticks, riding on aid trucks.

Israeli government spokesperson David Mencer told reporters that aid was continuing to enter from the south but did not specify whether any supplies were entering in the north.

The U.S.- and Israeli-backed Gaza Humanitarian Foundation, which operates aid distribution sites in southern and central Gaza, said on X that it was the only humanitarian organization permitted on Thursday to distribute food in Gaza.

A spokesperson said the foundation was exempt from a two-day suspension of humanitarian aid deliveries into the territory.

The Israeli prime minister's office and the defense ministry did not respond to Reuters' requests for comment.

The Higher Commission for Tribal Affairs, which represents influential clans in Gaza, said that trucks had been protected as part of an aid security process managed "solely through tribal efforts". The commission said that no Palestinian faction, a reference to Hamas, had taken part in the process.

Hamas, the militant group that has ruled Gaza for more than two decades but now controls only parts of the territory after nearly two years of war with Israel, denied any involvement.

Throughout the war, numerous clans, civil society groups and factions - including Hamas' secular political rival Fatah - have stepped in to help provide security for the aid convoys.

Clans made up of extended families connected through blood and marriage have long been a fundamental part of Gazan society.

ACUTE SHORTAGE

Amjad al-Shawa, director of an umbrella body for Palestinian non-governmental organisations, said the aid protected by clans on Wednesday was being distributed to vulnerable families.

There is an acute shortage of food and other basic supplies after the nearly two-year military campaign by Israel that has displaced most of Gaza's two million inhabitants.

Aid trucks and warehouses storing supplies have often been looted, frequently by desperate and starving Palestinians. Israel accuses Hamas of stealing aid for its own fighters or to sell to finance its operations, an accusation Hamas denies.

"The clans came ... to form a stance to prevent the aggressors and the thieves from stealing the food that belongs to our people," Abu Salman Al Moghani, a representative of Gazan clans, said, referring to Wednesday's operation.

The Wednesday video was shared on X by former Prime Minister Naftali Bennett, who claimed that Hamas had taken control of aid allowed into Gaza by the Israeli government. Bennett is widely seen as the most viable challenger to Netanyahu at the next election.

Netanyahu has also faced pressure from within his right-wing coalition, with some hardline members threatening to quit over ceasefire negotiations and the delivery of humanitarian aid.

The war began when Hamas launched a surprise attack on Israel on October 7, 2023, killing nearly 1,200 people, mostly civilians, and taking 251 others hostage into Gaza.

In response, Israel launched a military campaign that has killed more than 56,000 Palestinians, the majority of them civilians, according to local health authorities in Gaza.

At least 118 Palestinians have been killed by Israeli fire since Wednesday, local health authorities said, including some shot near an aid distribution point, the latest in a series of such incidents.

Twenty hostages remain in captivity in Gaza, while Hamas is also holding the bodies of 30 who have died.

(Reporting by Nidal al-Mughrabi in Cairo, Alexander Cornwell in Tel Aviv and Emma Farge in Geneva; Editing by Crispian Balmer, Philippa Fletcher and Gareth Jones)