The Israeli military says it carried out airstrikes on more than 320 targets in the Gaza Strip in the 24-hour period through Monday morning.

The military said the airstrikes destroyed underground tunnels, command centers and observation posts used by Hamas.

An NHK staff member in Gaza said the attacks on Sunday night were one of the most aggressive to date, with airstrikes taking place across the area. He also said some of the explosions were so powerful they felt like earthquakes.

Local media are reporting that the attacks killed about 400 people.

Sporadic fighting is taking place along the border between Israel and Gaza, where the Israeli military is amassing troops to prepare for a ground offensive.

An attack by an anti-tank missile left one Israeli soldier dead on Sunday.

On Monday, a spokesperson of the Israeli military was asked by reporters whether the ground offensive has been delayed because of a political decision.

The spokesperson replied that their job is to reduce threats to the operation and prepare in the best way possible during the time given.

The White House said on Sunday that President Joe Biden spoke with Israeli Prime Minister Benjamin Netanyahu over the phone.

The White House said Biden welcomed the first convoys of humanitarian aid arriving in Gaza and "the leaders affirmed that there will now be continued flow of this critical assistance into Gaza."

Meanwhile, Philippe Lazzarini, the commissioner-general of the UN Relief and Works Agency for Palestine Refugees, warned in a statement on Sunday that the agency will run out of fuel in three days.

He said, "Without fuel, there will be no water, no functioning hospitals and bakeries."

At least 1,400 people have died in Israel and more than 220 people were taken hostage since the clashes between Israel and Hamas began on October 7.

The death toll in Gaza has reached 4,651.