Israel's military denied striking a tent camp west of Rafah on Tuesday after Gazan health authorities said Israeli tank shelling had killed at least 21 people there, in an area Israel has designated a civilian evacuation zone.

The incident came two days after Israel's airstrike on tents housing displaced civilians in northwestern Rafah on Sunday, which resulted in the deaths of at least 45 Palestinians and injuries to numerous others.

The United States, Israel's closest ally, reiterated its opposition to the major Israeli ground offensive in Rafah but said it did not believe such an operation was underway. Describing the U.S. view of what would constitute a major offensive in Rafah, White House National Security Council spokesperson John Kirby told reporters that it would involve "large numbers of troops in columns and formations in some sort of coordinated maneuver against multiple targets on the ground."

"That is a major ground operation, we have not seen that," said Kirby, adding that there was nothing in the incidents on Sunday or on Tuesday that would prompt the U.S. to halt its military aid to Israel.

Nabil Abu Rudeineh, spokesperson for the Palestinian presidency, blamed the U.S. administration on Tuesday for the ongoing escalation in Rafah.

"We hold the U.S. administration fully responsible for the situation in Rafah and across Gaza," Abu Rudeineh told reporters in Ramallah, adding that the Israeli side ignored the ruling of an international court and has rendered the city "unlivable."

Abu Rudeineh criticized the U.S. administration's silence on Israeli actions, calling it an endorsement of what he labelled a "genocidal war" against Palestinians.

Earlier, defying an appeal from the International Court of Justice to stop its Rafah offensive, Israeli tanks advanced to the heart of city for the first time, while Spain, Ireland and Norway officially recognized a Palestinian state, a move that further deepened Israel's international isolation.

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

The UN Security Council held a meeting on Tuesday to discuss the deadly Sunday attack in Rafah at the request of Algeria. After the meeting, Algeria's UN Ambassador Amar Bendjama said the country would propose a draft UN resolution calling for an end to "the killing" in Rafah. 

"It will be a short text, a decisive text, to stop the killing in Rafah," Bendjama told reporters. 

So far, the Israeli military operation in besieged Gaza has killed more than 36,000 Palestinians, according to the Gazan health authorities. 

Egypt is again trying in tandem with Qatar and the U.S. to revive talks on a ceasefire and the release of hostages held by Hamas, but efforts have been hampered by Israel's assault on Rafah, Cairo's state-affiliated Al-Qahera News TV channel said on Tuesday, citing a senior official.

Hamas has said talks are pointless unless Israel ends its offensive in Rafah.

(With input from agencies)