Humanitarian aid getting into the Gaza Strip has increased by a large amount in the last few days, White House national security spokesman John Kirby said on Monday, adding the United States needs to see that aid sustained.

"The aid has increased and quite dramatically in just the last few days," Kirby said in an interview with MSNBC. "That's important but it has to be sustained."

More than 2,000 trucks have been able to get in, about 100 in the last 24 hours alone, Kirby said in an interview with MSNBC.

President Joe Biden earlier this month threatened to condition support for Israel's offensive in Gaza on it taking concrete steps to protect aid workers and civilians.

The move was prompted by an Israeli attack that killed seven World Central Kitchen aid workers. It was the first time the Biden administration has sought to leverage U.S. aid to influence Israeli military behavior.

As Biden said, Kirby added in a separate interview on CNBC, "Our policy with respect to Gaza will change if we don't see significant changes over time."

Six months into Israel's air and ground campaign in Gaza, triggered by Hamas' Oct. 7 attack on southern Israel, the devastated Palestinian enclave faces famine and widespread disease with nearly all its inhabitants now homeless.

Aid agencies have complained that Israel is not ensuring enough access for food, medicine and other needed humanitarian supplies.

(Reporting by Doina Chiacu; Editing by Chizu Nomiyama)