Palestinians inspect the site of an Israeli strike in Rafah, Gaza Strip, on Wednesday. Reuters

Israel's ambassador to the United Nations expressed disappointment Thursday at US President Joe Biden's threat to stop certain arms supplies to Israel if it invades the crowded Gaza city of Rafah.

"This is a difficult and very disappointing statement to hear from a president to whom we have been grateful since the beginning of the war," Gilad Erdan told Israeli public broadcaster Kan radio, in Israel's first reaction to Biden's warning.

Israel has defied international objections by sending in tanks and conducting "targeted raids" in the border city, which it says is home to Hamas's last remaining battalions -- but is also crowded with displaced Palestinian civilians.

"If they go into Rafah, I'm not supplying the weapons that have been used... to deal with the cities," Biden said in an interview with CNN, in his starkest warning to Israel since the start of the war.

"Civilians have been killed in Gaza as a consequence of those bombs," Biden said. "It's just wrong."

Erdan responded that Biden's comments would be interpreted by Israel's foes Iran, Hamas, and Hezbollah as "something that gives them hope to succeed".

"If Israel is restricted from entering an area as important and central as Rafah where there are thousands of terrorists, hostages and leaders of Hamas, how exactly are we supposed to achieve our goals?" he said.

"This is not a defensive weapon. This is about certain offensive bombs. In the end the State of Israel will have to do what it thinks needs to be done for the security of its citizens."

AFP journalists reported heavy shelling in Rafah early Thursday, and the Israeli military later said it was also striking "Hamas positions" further north in the centre of the Gaza Strip.

On Tuesday, Israeli forces seized Rafah's border crossing into Egypt, which has served the main entry point for aid into besieged Gaza.

Agence France-Presse