U.S. and European officials are preparing for a possible refugee wave out of Ukraine should Russia move forward with a full invasion of the Eastern European country – raising fears of a crisis that could eclipse the 2015 Syrian refugee crisis.

"If [Putin] employs that kind of combat power, it will certainly create enormous casualties within the civilian population and so this could create a … tragedy, quite frankly, in terms of refugee flow and displaced people," Defense Secretary Lloyd Austin said on ABC News on Sunday. "So this is potentially very, very dangerous."

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Russian President Vladimir Putin on Monday announced that he was recognizing two breakaway territories in Ukraine and followed it up with a deployment of troops that the White House has described as an "invasion." 

82nd Airborne Poland

U.S. troops of the 82nd Airborne Division, deployed to Poland because of the Russia-Ukraine tensions, set up camp at a military airport in Mielec, southeastern Poland, on Feb. 12, 2022. (AP Photo/Beata Zawrzel)

European countries have been warning for weeks that a flood of Ukrainian refugees could soon follow any invasion by Russia, raising fears of a flood of people that could cause knock-on effects in nearby countries and the continent as a whole. Those fears are shared by American officials.

"If Russia invades Ukraine even further, we will see a devastating loss of life, unimaginable suffering. Millions of displaced people will create a refugee crisis across Europe," U.N. Ambassador Linda Thomas-Greenfield said Monday at the U.N. Security Council.

Poland, the largest E.U. nation to border Ukraine, said earlier this month that it has been making plans to accept refugees, including internal scenarios and infrastructure. Plans include housing refugees in hostels and sports facilities. The Associated Press reported that local mayors have been asked to draw up reports of what facilities could be made available.

"In this worst-case scenario, we are not talking about hundreds or thousands, but much larger numbers," Marcin Przydacz, a deputy foreign minister, said on Radio Plus.

The New York Times reported this week that many of the thousands of U.S. troops currently in Poland are working with the country’s armed forces to set up processing centers for tens of thousands of people who may flee Ukraine. The outlet reported that Pentagon estimates say that up to 5 million refugees could pour into neighboring countries in the event of a national attack on Ukraine.

That would be more than the approximately one million refugees from Syria and other nearby countries who hit Europe in the wake of the 2015 refugee crisis – a crisis that led to dramatic political upheavals as the continent struggled to cope.

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In Hungary, which was on the front lines of the 2015 crisis and eventually erected strict immigration and border controls, said this week it will deploy soldiers and equipment to the region near the Ukrainian border to prepare for armed groups attempting to enter – as well as the possibility of Ukrainian refugees.

The latest risk comes after the E.U. faced a crisis on the border between Belarus and Poland in November that threatened to boil over. European officials accused Belarus President Alexander Lukashenko of creating a crisis by funneling thousands of migrants to the border in retaliation for sanctions imposed on his government after a crackdown on dissent and a stolen 2020 election victory. That raised concerns that it was being orchestrated by Putin, an ally of Lukashenko, to destabilize Europe by tapping into a still-thorny issue.

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The U.S. recently faced a refugee surge out of Afghanistan after it withdrew from the country at the end of August. That resulted in tens of thousands of Afghans being relocated into the United States – a resettlement that was recently found to have issues in its vetting.

However, there has been no indication that the Biden administration is planning for a mass relocation of refugees to the United States itself in the event of a deeper invasion into Ukraine by Russia.

The Associated Press contributed to this report.