At least 21 people were killed after a new Israeli strike targeted the evacuation zone of a displacement camp west of Rafah on Tuesday, just two days after Israel's outrageous attack, which killed at least 45 people, led to global condemnation.

Mohammad al-Mughayyir, a senior official at the agency, said 21 people had been killed in an "occupation strike targeting the tents of displaced people west of Rafah."

Palestinian resistance group Hamas also said an Israeli strike had caused "dozens of martyrs and wounded" in the area.

Gaza emergency services said four tank shells hit a cluster of tents in Al-Mawasi, a coastal area that Israel had advised civilians in Rafah to move to for safety.

At least 12 of the dead were women, according to medical officials in the Hamas militant-run Palestinian enclave. An Israeli military spokesperson said: "As of this time, we are not aware of this incident." Israeli officials have made it a habit to act like they are not aware of civilian casualties or try to cover up their war crimes by saying the areas they hit are Hamas hideouts, despite damning evidence proving otherwise.

In central Rafah, tanks and armored vehicles mounted with machineguns were spotted near Al-Awda mosque, witnesses told Reuters. The Israeli military said its forces continued to operate in the Rafah area, without commenting on reported advances into the city center.

International uproar over Israel's three-week-old Rafah offensive has turned to outrage after an attack on Sunday set off a blaze in a tent camp in a western district of the city, killing at least 45 people.

Global leaders voiced horror at the fire in a designated "humanitarian zone" of Rafah where families uprooted by fighting elsewhere had sought shelter and urged the implementation of a World Court order last week for a halt to Israel's assault.

Tuesday's attack occurred in an area designated by Israel as an expanded humanitarian zone, to which it had called on civilians in Rafah to evacuate for their own safety when it launched its incursion in early May.

In a diplomatic move purportedly aimed at reining in the violence, Spain, Ireland and Norway officially recognized a Palestinian state on Tuesday.

The three countries have said they hope their decision will accelerate efforts toward securing a cease-fire in Israel's war against Palestinians, now in its eighth month, that has reduced much of the densely populated territory to rubble.

Residents said Rafah's Tel Al-Sultan neighborhood, the scene of Sunday's night-time strike in which tents and shelters were set ablaze as families settled down to sleep, was still being bombarded.

"Tank shells are falling everywhere in Tel Al-Sultan. Many families have fled their houses in western Rafah under fire throughout the night," one resident told Reuters via a chat app.

Around one million people - many repeatedly displaced by shifting waves of the war - have fled the Israeli offensive in Rafah since early May, the U.N. agency for Palestinian refugees (UNRWA) reported on Tuesday.

A video obtained by Reuters showed families on the move again, carrying their belongings through Rafah's shattered streets, their weary children trailing behind them.

"There are a lot of attacks, smoke and dust. It is death from God...The (Israelis) are hitting everywhere. We're tired," said Moayad Fusaifas, pushing along belongings on two bicycles.

Israel has kept up its merciless attacks despite the ruling by the International Court of Justice on Friday ordering it to stop given the high risk of civilian casualties.

More than 36,000 Palestinians, mostly women and children, have been killed in Israeli attacks, Gaza's health ministry says.

In some residential districts from which Israeli forces have retreated, civil emergency teams said they were recovering bodies from the ruins.