Vice President Kamala Harris on Sunday called for an “immediate cease-fire” in Gaza, saying that Hamas should agree to the six-week pause currently on the table and that Israel should increase the flow of aid into the besieged enclave amid a humanitarian crisis.

Ms. Harris’s remarks, delivered in Selma, Ala., bolstered a recent push by the Biden administration for an agreement and came a day before she was to meet with a top Israeli cabinet official involved in war planning, Benny Gantz. Her tone, sharper and more urgent than President Biden’s in recent days, showed the White House’s building frustration with Israel. Last month the president called Israel’s response to the Oct. 7 Hamas-led attack “over the top.”

Ms. Harris also assailed what she called a “humanitarian catastrophe” in Gaza and pressed Israel to allow for the increase of aid into the besieged enclave.

Ms. Harris was in Selma on Sunday for the 59th anniversary of Bloody Sunday. Her comments on Israel were her most forceful to date on the Middle East conflict, which has killed more than 30,000 Palestinians, according to Gazan health authorities, and put the enclave on the brink of famine.

“People in Gaza are starving,” Ms. Harris said. “The conditions are inhumane. And our common humanity compels us to act.”

She added: “Given the immense scale of suffering in Gaza, there must be an immediate cease-fire.” That line drew loud applause from the crowd that had gathered to mark the civil rights event.

Ms. Harris reiterated the Biden administration’s support for a six-week cease-fire, which would allow for a pause in fighting and the release of Israeli hostages taken during the attack in Israel. U.S. officials said this weekend that Israel had all but signed on to the deal, but Hamas has yet to agree to it.

Ms. Harris restated the United States’ support for Israel’s right to defend itself against the ongoing threat by Hamas, which she said had no regard for innocent life in Israel or in Gaza.

She also said that Israel must do more to allow for the flow of aid into Gaza, including opening borders, lifting any unnecessary restrictions on aid deliveries and restoring services to Gaza.

“The Israeli government must do more to significantly increase the flow of aid,” she said. “No excuses.”

The remarks came as Ms. Harris was scheduled to meet with Mr. Gantz, a member of the Israeli war cabinet, at the White House on Monday, and as the Biden administration faces immense pressure to limit the carnage in Gaza.