WASHINGTON — Ukrainian President Volodymyr Zelensky in a speech to members of Congress on Wednesday compared the carnage raining down on his country to Pearl Harbor and 9/11, invoking some of the most horrific moments in American history as he urged the United States to establish a no-fly zone in Ukraine.

“Our country experiences the same every day, right now, at this moment, every night for three weeks,” Zelensky said in the speech delivered by video to hundreds of members of Congress watching from an auditorium in the Capitol. “Russia has turned the Ukrainian sky into a source of death for thousands of people.”

Speaking in Ukrainian and through a translator, he turned to another signature moment in U.S. history, citing the Rev. Dr. Martin Luther King Jr.’s “I Have a Dream” speech as he pleaded, “I have a need.”

“I need to protect our sky,” Zelensky said, wearing an olive green T-shirt, unshaven, and seated against a plain white backdrop, with the edge of a blue and yellow Ukrainian flag visible to his side. “I need your decision, your help.”

He thanked America for its military aid and sanctions against Russia. But he switched to English as he concluded his speech by urging President Joe Biden to do more.

“You are the leader of the nation,” Zelensky said. “I wish you to be the leader of the world. Being the leader of the world means to be the leader of peace.”

Hours later, Biden laid out his latest steps to help Ukraine, in remarks prepared before Zelensky’s speech. He said the United States will send $800 million more in military assistance, for a total of $2 billion since he took office, $1 billion in the last week. Biden said the new assistance includes 800 Stinger antiaircraft systems, 100 grenade launchers, 20 million rounds of small-arms ammunition, and grenade launchers, mortar rounds, and an unspecified number of drones.

“We are united in our abhorrence of Putin’s depraved onslaught, and we’re going to continue to have their backs as they fight for their freedom, their democracy, their very survival,” Biden said at the White House. He didn’t directly address the criticism that the United States should be doing more.

Zelensky spoke to members of Congress as his country faces a brutal and unprovoked assault that Ukrainian officials say has left thousands dead, including many civilians and children killed as Russian targets include homes, escape routes, and hospitals.

At one point he played a video contrasting scenes of Ukrainians at play with devastating and gut-wrenching images of destruction. It showed artillery strikes hammering residential buildings, children and mothers in tears, people lying dead in ruined streets, bodies hauled into mass graves, a pair of small empty shoes, a man bent in grief over a body on a gurney, and a tiny toe pointing out from beneath a bloody sheet.

Some lawmakers shook their heads and wiped eyes as they watched in silence.

Zelensky, a former comedian, has become the global face of Ukrainian resistance, his haggard social media posts from Kyiv emblematic of his country’s resistance to the Russian aggression. He has used his standing to issue calls for not just moral support but military aid.

Members of Congress, many wearing lapel pins with Ukrainian and American flags, greeted him with a standing ovation. They listened from blue velvet chairs in a Capitol auditorium, joined by the Ukrainian ambassador to the United States, Oksana Markarova.

“He’s a modern-day Churchill,” said Rep. Brian Fitzpatrick (R., Pa.), the cochair of the Congressional Ukraine Caucus. “He’s a guy who’s ready to stay and die for his country.”

And he called for the U.S. and its allies to go beyond the steps it has already taken. Fitzpatrick, a member of the House Foreign Affairs Committee, said he would favor using United Nations forces to create a no-fly zone over humanitarian escape corridors, a move the Biden administration and many lawmakers worry could pull the U.S. into the war.

“The alternative is — we just witnessed — continued slaughtering of innocent civilians,” Fitzpatrick said after the speech. “That’s the alternative. And that’s not a viable alternative for me. There’s no no-risk options here. There’s a risk of inaction as well. So my belief is that Putin will not stop until somebody stops him.”

But Biden and many members of Congress have warned against establishing no-fly zones over Ukraine, fearing that a direct military clash with Russia would escalate the war, draw in U.S. forces, and risk spreading the conflict even more widely.

In Philadelphia last week, Biden warned Democratic House members that such an outcome would lead to “World War III.”

Zelensky spoke to Congress a day after addressing Canadian lawmakers with a similar appeal, and last week he spoke to the British Parliament. In early March he had addressed American lawmakers in a private Zoom call.

While many members of both parties share Biden’s wariness about no-fly zones, Republicans said he could be doing more for Ukraine.

Sen. Pat Toomey (R., Pa.) said he’s “not comfortable” with the idea of American forces patrolling Ukrainian skies and potentially clashing with Russian fighters.

“But there’s a lot we could be doing short of that,” Toomey said, including supplying fighter jets to Ukraine. “The man wants the MiGs that are available to him. He should have that.”

Some Defense Department officials have raised questions about how meaningful a handful of jets would be, and have warned they may have been modified so much that Ukrainian pilots might not be able to use them. But Toomey rejected other concerns that supplying jets would risk escalation.

“Putin can just roll into a country and start murdering people by the tens of thousands, and we’re going to be worried about being provocative? It’s ridiculous,” he said.

Sen. Cory Booker (D., N.J.), a member of the Senate foreign relations committee, said Zelensky “struck chords that speak to the universal principles we share in common.” But asked about a no-fly zone, he pointed to previous steps Congress has taken, adding that U.S. efforts to protect Ukraine “have to be balanced” with “making sure we do not trigger an expansion of the war into all of Europe and beyond.”

Rep. Tom Malinowski (D., N.J.) saw the no-fly zone as part of a push for other aid that Zelensky knows is more likely to come.

“The no-fly zone request is to make us feel guilty that we can’t do the no-fly zone, so that we work even harder on everything that we can do,” said Malinowski, a member of the House Foreign Affairs Committee. “It’s brilliant. It’s exactly what he should be doing.”

But Fitzpatrick argued that the U.S. could do more. He visited Poland earlier this month and saw some of the thousands of Ukrainian refugees fleeing their country.

He called Wednesday for giving Zelensky “all the defensive equipment he needs” and not drawing distinctions between items that might be considered offensive rather than defensive.

“What I’ve shared with all my colleagues is if you feel an incredible sense of guilt from what you’re seeing on TV, you need to unpack that,” Fitzpatrick said. “There’s a reason why you feel guilty: It’s because there’s things that we could be doing that we’re not.”

The Associated Press contributed to this article.