US, NATO 'would respond' if Putin used chemical weapons in Ukraine, Biden says

President Joe Biden took questions at a news conference at NATO headquarters in Brussels, addressing warnings of a possible chemical weapons attack by Russia in Ukraine, after meeting with European leaders Thursday and following Ukraine's President Zelenskky pleading with them to do more to help.

Noting Biden has warned there's a "real threat" in Russia using chemical weapons in Ukraine, the first question to him was on whether the U.S. has gathered specific intelligence that suggests that Russian President Vladimir Putin is considering deploying chemical weapons and whether the U.S. or NATO respond with military action if he did use them.

"I'm not going to give you intelligence data, number one," Biden said. "Number two, we would respond. We would respond if he uses it, and the nature of the response would depend on the nature of the use."

ABC News Chief White House Correspondent Cecilia Vega followed up, and asked, "If chemical weapons were used in Ukraine could that trigger a military response from NATO?"

"It would trigger a response in kind," Biden replied. "Whether or not -- you're asking whether NATO would cross -- we'd make that decision at the time."

But Biden did not lay out what that response might look like and whether it would involve sending U.S. troops to Ukraine, which Biden has vowed not to do.

As he began, Biden announced a range of new sanctions against Russia targeting the majority of the Duma and Russian elites, that the U.S. will welcome up to 100,000 refugees from Ukraine and provide $1 billion in new humanitarian aid, as he faces pressure from Zelenskyy to provide more deliverables to Ukraine.

"Putin is getting exactly the opposite of what he intended to have as a consequence of going into Ukraine," Biden said, adding later on that he was "banking on NATO being split."

Biden also described his call last week with China's President Xi Jinping as "very straightforward" and said that, while "I made no threats," he did make clear Xi would be "putting himself in significant jeopardy" if China helped Russia with its invasion of Ukraine.

The president made the foreign trip to attend an extraordinary summit of all 30 NATO leaders to reaffirm the U.S. commitment to NATO allies, participate in a pre-scheduled meeting of the European Council -- the political body of the European Union -- and meet with leaders of the Group of Seven, or G-7, major industrial nations.

Biden also answered a definitive "yes," when asked he believes that Russia should be removed from the G20, but noted that it "would depend on the G20" to make that decision.

He said that point was raised today by G20 leaders and that he raised the possibility that if removing Russia can't be done because of "Indonesia and others" not in agreement, Ukraine should be able to attend future G20 meetings.

And when he was asked if Zelenskyy needs to cede any Ukrainian territory in order to gain a cease-fire with Russia, Biden said, "that is a total judgment based on Ukraine."

According to senior U.S. administration officials, the mood at NATO's emergency summit has been "sober" and "resolute" so far.

"There was a very strong sense that we are facing a significant historical moment, and very strong support from all the leaders who spoke about the need to defend our democracy," one of the officials told reporters during a telephone briefing Thursday.

The officials said Zelesnkyy, who addressed NATO leaders remotely, spoke "very eloquently" and "repeated his requests for continued and increased Western security assistance."

"But notably, there was not a request for a no-fly zone," an official added. "There was also not a request for NATO membership."

Zelesnkyy did ask for NATO to give 1% of all its tanks and said he hasn't been given an answer.

"I have been repeating the same thing for a month now: To save people and our cities, Ukraine needs military assistance without restrictions, as Russia uses without restrictions its entire arsenal against us," he continued. "Ukraine asked for your planes so that we do not lose so many people. And you have thousands of fighter jets, but we haven't been given any yet."

"We asked for tanks so that we can unblock our cities that are now dying," he added. "You have at least 20,000 tanks. Ukraine asked for a percent -- 1% -- of all your tanks to be given or sold to us. But we do not have a clear answer yet."

Speaking after Zelenskyy's speech, Biden that Thursday marks one month since Russia launched its invasion of Ukraine. He discussed the sanctions that have already been imposed and expressed strong support for Ukraine as well as humanitarian and military aid and reaffirmed his support for Article 5, which is the cornerstone of NATO and states that an attack on one member is an attack on all members.

Since Russian President Vladimir Putin launches his invasion one month ago, 3.5 million Ukrainians have fled the country and millions more have become internally displaced.

Biden is scheduled to travel to Poland on Friday.

As the fighting continues, Secretary of State Antony Blinken announced on Wednesday that the State Department has made a formal assessment that Russian forces have committed war crimes in Ukraine.

ABC News' Ben Gittleson, Conor Finnegan, Sarah Kolinovsky, and Justin Gomez contributed to this report.