A long line of blocked relief trucks on Egypt's side of the border with the Gaza Strip where people face starvation is a moral outrage, UN Secretary-General Antonio Guterres said during a visit to the Rafah crossing on Saturday.

It was time for Israel to give an "ironclad commitment" for unfettered access to humanitarian goods throughout Gaza, said Guterres, who also called for an immediate humanitarian ceasefire and the release of Israeli hostages held in Gaza.

The UN would continue to work with Egypt to "streamline" the flow of aid into Gaza, he said in comments made in front of the gate of the Rafah crossing, an entry point for aid.

"Here from this crossing, we see the heartbreak and heartlessness of it all. A long line of blocked relief trucks on one side of the gates, the long shadow of starvation on the other," he said. "That is more than tragic. It is a moral outrage."

The visit by Guterres comes as Israel faces global pressure to allow more humanitarian aid into Gaza, which has been devastated by more than five months of war between Israel and Hamas.

Israel, which has vowed to destroy Hamas and is worried that the Palestinian militant group will divert aid, has kept all but one of its land crossings into the enclave closed. It opened its Kerem Shalom crossing close to Rafah in late December and denies accusations by Egypt and UN aid agencies that it has delayed deliveries of humanitarian relief, saying the UN has failed to distribute aid within Gaza.

Israeli Foreign Minister Israel Katz criticised Guterres in a social media post for blaming Israel "without condemning in any way the Hamas-ISIS terrorists who plunder humanitarian aid".

In remarks made later to reporters, Guterres also reinforced international appeals against an Israeli ground operation in Rafah city on the Gazan side of the border, where a majority of Gaza's 2.3 million residents are sheltering. He questioned Israeli plans to relocate civilians ahead of an incursion.

"It is extremely doubtful any successful programme to provide security and safety for the population of Rafah when that security and safety doesn't exist in the whole of the Gaza territory," he said. (Reuters)