U.S. President Joe Biden and Western allies opened the first of three summits Thursday focused on increasing pressure on Russian President Vladimir Putin over his war in Ukraine while tending to the economic and security fallout spreading across Europe and the world.

Biden and the leaders of other NATO countries met at the alliance’s headquarters where they posed for a group photo memorializing the urgent gathering before retreating behind closed doors for their summit, which was expected to last several hours.

Over the course of Thursday, the European diplomatic capital is hosting an emergency NATO summit as well as a gathering of the Group of Seven industrialized nations and a summit of the 27 members of the European Union. Biden will attend all three meetings and plans to hold a news conference at the end of the day.

Biden arrived here late Wednesday with the hopes of nudging allies to enact new sanctions on Russia, which has already seen its economy crippled by a steady stream of bans, boycotts and penalties over the past four weeks.

While the West has been largely unified in confronting Russia after it invaded Ukraine, there’s wide acknowledgement that unity will be tested as the costs of war chip at the global economy.

The bolstering of forces along NATO’s eastern flank, almost certainly for at least the next 5-10 years if Russia is to be effectively dissuaded, will also put pressure on national budgets.

“We need to do more, and therefore we need to invest more. There is a new sense of urgency and I expect that the leaders will agree to accelerate the investments in defense,” said NATO Secretary-General Jens Stoltenberg before chairing the security alliance’s summit.

En route to Brussels aboard Air Force One, Biden’s national security adviser, Jake Sullivan, told reporters that “what we would like to hear is that the resolve and unity that we’ve seen for the past month will endure for as long as it takes.”

The energy crisis exacerbated by the war will be a particularly hot topic at the European Council summit, where leaders from Spain, Portugal, Italy and Greece are hoping for an urgent, coordinated bloc-wide response. EU officials have said they will seek U.S. help on a plan to top up natural gas storage facilities for next winter, and they also want the bloc to jointly purchase gas.

German Chancellor Olaf Scholz has dismissed calls to boycott Russian energy supplies, saying it would cause significant damage to his country’s economy. Scholz is facing pressure from environmental activists to quickly wean Germany off Russian energy, but he said the process will have to be gradual.

“To do so from one day to the next would mean plunging our country and all of Europe into recession,” Scholz said Wednesday.

Poland and other eastern flank NATO countries will also be looking for clarity on how the United States and fellow European nations can assist in dealing with their growing concerns about Russian aggression as well as a spiraling refugee crisis. More than 3.5 million refugees have fled Ukraine in recent weeks, including more than 2 million to Poland.

Biden is scheduled to travel to Poland on Friday, where both issues are expected to be at the center of talks with President Andrzej Duda. Another significant moment could come shortly before Biden returns to Washington on Saturday. The White House said he plans to “deliver remarks on the united efforts of the free world to support the people of Ukraine, hold Russia accountable for its brutal war, and defend a future that is rooted in democratic principles.”

Sullivan said that Biden and fellow leaders would aim to “set out a longer-term game plan” for what forces and capabilities are going to be required for the alliance’s eastern flank countries.

Four new NATO battlegroups, which usually number between 1,000-1,500 troops, are being set up in Hungary, Slovakia, Romania and Bulgaria.

Ukrainian President Volodymyr Zelenskyy, who is expected to address the NATO summit by video, said late Wednesday that he wants the alliance to “declare that it will fully assist Ukraine to win this war” by supplying any weapons necessary.

All the while, national security officials from Washington to Warsaw are increasingly worried that Putin might deploy chemical, biological or even nuclear weaponry. Sullivan said the allies would consult on how to respond to “potential contingencies” of that sort, including “this whole question of the potential use of nuclear weapons.”

Biden, before departing for Brussels on Wednesday, told reporters that he believed the possibility of Russia deploying chemical weapons was a “real threat.”

Stoltenberg would not be drawn Thursday on whether such a strike is a red line that would draw the alliance into war with Russia. “I will not speculate beyond the fact that NATO is always ready to defend, to protect and to react to any type of attack on a NATO allied country,” he said.

Kremlin spokesman Dmitry Peskov in a CNN interview this week said that Russia could consider using its nuclear weapons if it felt there was “an existential threat for our country.”

The head of the European Union’s executive arm said she wanted to discuss with Biden the possibility of securing extra deliveries of liquefied natural gas from the United States for the 27-nation bloc.

Speaking at the European Parliament ahead of Biden’s visit, Ursula von der Leyen said the EU was seeking a a commitment for additional LNG supplies from the U.S. “for the next two winters.”

The EU imports 90% of the natural gas used to generate electricity, heat homes and supply industry, with Russia supplying almost 40% of EU gas and a quarter of its oil. The bloc is looking at ways to reduce its dependence on Russian gas by diversifying suppliers.

Sullivan said the United States was looking for ways to “surge” LNG supplies to Europe to help make up for supply disruptions.

Biden, for his part, was expected to detail plans for new sanctions against Russia and humanitarian assistance for the region.

One new sanctions option that Biden is weighing is to target members of the Russian State Duma, the lower house of parliament, according to a U.S. official who spoke on the condition of anonymity to discuss private deliberations. The official added that a final decision hadn’t been made and that the new sanctions would be rolled out in coordination with Western allies.

Biden arrived in Brussels with Americans increasingly accepting of the need for the U.S. to play a role in stopping in Putin, according to a poll from The Associated Press-NORC Center for Public Affairs Research.

But even as concern among Americans has swelled and and support for a major U.S. role in the conflict strengthened in the last month, Biden’s negative approval rating has not budged, the AP-NORC poll found. Few are very confident that he can handle a crisis, and a majority thinks he lacks toughness in dealing with Russia.

Biden promised voters that he had the experience to navigate a complicated international emergency like the one unfolding in Europe now, and his trip will be the latest test of that proposition as he tries to maintain unity among Western allies and brace for potentially even bigger challenges.

At a time when it is essential to avoid fissures in what’s been a largely unified Western response to Russia, the U.S. president will look to press important allies like Poland to dial back the idea of deploying a Western peacekeeping mission to Ukraine. It’s an idea that the U.S. and some other NATO members see as too risky as they seek to deny Russia any pretext to broaden the war beyond Ukraine’s borders.

For his domestic audience, Biden is expected to once again underscore the heroics of the Ukrainian military and volunteers who have managed to hold off an imposing Russian military. He will highlight those remarkable efforts — as well as the generosity of the Poles and other allies at the front lines of the humanitarian crisis — as he redoubles his calls for Americans to stand firm against a Russian war that is spurring gas price hikes and adding to inflationary pressures in the U.S.

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Madhani reported from Washington. Associated Press writers Matthew Lee, Hannah Fingerhut and Darlene Superville in Washington and Samuel Petrequin in Brussels contributed to this report.

AP