CAIRO (Reuters) - More than 100 aid trucks managed to reach the Gaza Strip by Monday morning after an agreement to reroute aid through the Kerem Shalom border crossing, but supplies have not been distributed amid an ongoing Israeli assault, sources said.

Deliveries are badly needed as little aid has reached southern Gaza since May 6, when Israel took control of the Palestinian side of the Rafah border crossing, about 3.5 km from Kerem Shalom and the main entry point into Gaza for humanitarian and commercial supplies.

The latest arrivals would be the biggest aid delivery into southern Gaza by far since the launch of Israel's attacks in Rafah, with most days seeing no trucks crossing the border.

Israeli forces began a ground offensive in the east of Rafah over three weeks ago. An Israeli airstrike on Sunday triggered a fire that killed 45 people in a tent camp in Rafah, officials said on Monday, prompting an outcry from global leaders.

Egyptian security sources told Reuters that 123 aid trucks had crossed the border and handed over the goods to the United Nations. An Israeli source confirmed that aid had been brought into the Gaza side and handed over to partners.

An Egyptian aid source said that four fuel trucks had also crossed the border.

But Palestinian trucks that went to pick up the aid at the crossing returned empty, U.N. and Palestinian officials told Reuters.

"Trucks moved through but it was not possible to collect them due to the rocket attacks yesterday and the IAF (air force) strikes overnight," said a U.N. official in Gaza, adding that the supplies belonged to the U.N.'s Palestinian aid agency UNRWA and the World Food Programme.

On Friday, Egypt and the United States agreed to utilise Kerem Shalom until arrangements were made to re-open Rafah from the Palestinian side, the Egyptian presidency said. Egypt has refused to coordinate with Israel on the crossing.

About 200 trucks were expected to come in on Sunday, still below what officials say is needed in the strip, home to 2.3 million people, where monitors say famine in some parts is imminent.

KSrelief, a Saudi-funded charity, on Monday sent a ship carrying nearly 500 tonnes of aid including food, medical supplies and shelter material for Gaza, the group's supervisor general Abdullah Al Rabeeah told Reuters.

It is due to arrive at Egypt's El Arish port within a day and then be offloaded for eventual delivery in southern Gaza.

(Reporting by Ahmed Mohamed Hassan and Nidal Al Mughrabi in Cairo, Yusri Mohamed in Ismailia, Emma Farge in Geneva; writing by Nafisa Eltahir; editing by Nick Macfie)