Trump hints at 'action' if Hamas doesn't return hostage bodies

The United Nations' World Food Programme said it is "scaling up its operations in Gaza" as the ceasefire has gone into effect.

Since Saturday, 137 trucks with food aid have gone into Gaza "to support bakeries, nutrition programmes and general food distributions," the organization said in a release Tuesday.

"With full access, WFP intends to restore its regular food distribution system, scaling assistance through 145 distribution points across the Strip," the organization said.

-ABC News' Ellie Kaufman

The remains of four more hostages have been handed over to Israel.

Four coffins of deceased hostages, escorted by Israeli forces, crossed the border into Israel, headed to the National Institute for Forensic Medicine, where officials will carry out identification procedures.

There are still believed to be 20 hostage bodies remaining in Gaza.

The United Nations and other aid organizations “have been able to move more freely across parts of Gaza from which Israeli forces have withdrawn,” since the first phase of the ceasefire deal went into effect, U.N. Deputy spokesperson for the Secretary General Farhan Haq said at a press briefing at U.N. headquarters in New York Tuesday.

"This improved access has allowed partners to scale up the response to the most urgent needs," Haq said.

World Health Organization teams reached Al Ahli Hospital with eight trucks of medical supplies on Monday, and their teams reached the European Hospital in Khan Younis to transfer critical medications and intensive care unit equipment to Nasser Hospital, Haq said.

"The U.N. and our humanitarian partners have also installed a solar panel for a desalination unit in Deir al Balah, as well as new telecommunications hardware to improve connectivity for affected people and humanitarian operations," Haq said.

Members of the International Committee of the Red Cross are on their way to retrieve the remains of several hostages held by Hamas in the southern Gaza Strip, according to the Israel Defense Forces.

It is unclear how many remains will be handed over.