A number of top national security officials are involved in discussions with President Biden as he weighs sending several thousand U.S. troops to Eastern Europe and the Baltic States amid the possibility of a Russian invasion of Ukraine.

Involved in the discussions are: 

White House national security adviser Jake Sullivan

Sullivan serves as the national security adviser to President Biden. He was also Biden’s national security adviser when he was vice president and served as an adviser on Hillary Clinton’s 2016 presidential campaign as well. During the first term of the Obama administration, when Clinton was secretary of state, Sullivan served as her chief of staff at the State Department.  

(AP Photo/Susan Walsh; Jonathan Ernst/Pool via AP; AP Photo/Susan Walsh; AP Photo/Susan Walsh)

Defense Secretary Lloyd Austin

Austin, as defense secretary, is the principal assistant to the president in all matters relating to the Department of Defense and serves on the National Security Council. Previously, Austin served as commander of U.S. Central Command responsible for all military operations in the Middle East and Afghanistan. He retired from the Army in April 2016. Austin has been criticized for the Biden administration’s botched withdrawal of U.S. troops from Afghanistan in August 2021.

Chairman of the Joint Chiefs of Staff Gen. Mark Milley

Milley has served as the chairman of the Joint Chiefs of Staff, which is the nation’s highest-ranking military officers, and the principal military adviser to the president, Secretary of Defense Lloyd Austin and the National Security Council, since October 2019. Milley previously served as the chief of staff of the U.S. Army. Milley too has been criticized for the Biden administration’s Afghanistan withdrawal.

Secretary of State Antony Blinken

Blinken previously served as deputy secretary of state for former President Obama from 2015 to 2017. Before that, Blinken served as Obama's principal deputy national security adviser. During Obama's first term, Blinken served as then-Vice President Biden's national security adviser. From 2001 to 2003, and then 2007 to 2009, he worked as Democratic staff director for the Senate Foreign Relations Committee, which then-Sen. Joe Biden chaired. During the Clinton administration, Blinken served as a member of the National Security Council staff and served as the president’s principal adviser on the countries of Europe, the European Union, and NATO. 

Director of National Intelligence Avril Haines

Haines is the first woman to lead the U.S. Intelligence Community. During the Obama administration, Haines served as assistant to the president and principal deputy national security adviser. Haines also served as the deputy director of the Central Intelligence Agency from 2013 to 2015.

CIA Director William Burns

Burns, who leads the Central Intelligence Agency, previously served as the deputy secretary of state from 2011 through 2014, and as the undersecretary for political affairs from 2008 to 2011. Burns served as the U.S. ambassador to Jordan from 1998 to 2001, and the U.S. ambassador to the Russian Federation from 2005 to 2008.

U.S. Ambassador to the United Nations Linda Thomas-Greenfield

Thomas-Greenfield previously served as the assistant secretary of state for African affairs from 2013 to 2017. Prior to that appointment, she served as director general of the Foreign Service and Director of Human Resources at the State Department. She also served as U.S. ambassador to Liberia, and posted at the U.S. Mission to the United Nations in Geneva, Pakistan, Kenya, The Gambia, Nigeria, and Jamaica. 

Counselor to the president Steve Ricchetti

Ricchetti previously served as Biden's chief of staff while he served as vice president during the Obama administration. He also served as deputy chief of staff for operations under former President Clinton.  

The officials, over the weekend, presented the president with various options to respond to Russia’s aggressive stance in Eastern Europe. Officials met in person and virtually with the president during a Sunday briefing at Camp David.

The president is now considering sending 3,000 to 5,000 U.S. troops to Romania and to Latvia, Lithuania, and Estonia as part of a broader NATO effort. Other NATO countries may also contribute troops to warn Russian President Vladimir Putin not to try to move into neighboring countries.

As part of the effort, Biden is also considering deploying naval vessels for NATO allies who may feel threatened. Some equipment and troops in these proposed actions would come from Europe and some would come from the U.S.

At this point, NATO said that it is "sending additional ships and fighter jets" to Eastern Europe. This includes F-16s from Denmark, naval forces from Spain, and F-35s from The Netherlands. France is ready to send troops to Romania, which borders Ukraine to the south. 

Over the weekend, the State Department ordered the evacuation of American citizens in Ukraine amid the threat of Russian military action. Officials also ordered family members of employees at the United States Embassy in Kyiv to leave the nation on Monday.

NATO SENDING FIGHTERS, SHIPS TO REGION; UK TO WITHDRAW SOME STAFF FROM EMBASSY IN UKRAINE

"U.S. citizens in Ukraine should be aware that Russian military action anywhere in Ukraine would severely impact the U.S. Embassy’s ability to provide consular services, including assistance to U.S. citizens in departing Ukraine," the State Department said in a travel advisory.

The State Department said in the travel advisory that eligible family members are being ordered to leave the country, while U.S. citizens in Ukraine should "consider" leaving the country.

"On January 23, 2022, the Department of State authorized the voluntary departure of U.S. direct hire employees and ordered the departure of eligible family members from Embassy Kyiv due to the continued threat of Russian military action. U.S. citizens in Ukraine should consider departing now using commercial or other privately available transportation options," the advisory reads.

According to the travel advisory, security conditions in Ukraine can "deteriorate with little notice."

"There are reports Russia is planning significant military action against Ukraine. The security conditions, particularly along Ukraine’s borders, in Russia-occupied Crimea, and in Russia-controlled eastern Ukraine, are unpredictable and can deteriorate with little notice," the advisory states.

That announcement came after the U.K.'s Foreign, Commonwealth & Development Office announced on Saturday that it had information suggesting that the Russian government is plotting to install a pro-Kremlin leader in Kyiv.

STATE DEPARTMENT ISSUES ‘DO NOT TRAVEL’ WARNING FOR UKRAINE AS EMBASSY STAFF IS TOLD TO LEAVE 

But on Monday, the Ukrainian Ministry of Foreign Affairs accused the United States of "excessive caution" for ordering family members of Kyiv Embassy staff to leave the country, as Russia gets closer to invading Ukraine by the day. 

"We have taken note of @StateDept’s decision re departure of family members of @USEmbassyKyiv staff," Ukraine spokesman Oleg Nikolenko tweeted. "While we respect right of foreign nations to ensure safety & security of their diplomatic missions, we believe such a step to be a premature one & an instance of excessive caution."

The United Kingdom is also bringing home "Some Embassy staff and dependents" due to the "growing threat from Russia." 

BLINKEN DODGES QUESTION ON SENDING U.S. TROOPS TO UKRAINE

Ukraine's territory has long been in Putin's crosshairs, especially amid recent NATO considerations of potentially allowing Ukraine to join the alliance. It is one of several post-Soviet republics in the region that shifted toward an alliance with the West after the collapse of the Soviet Union. 

Putin was in the Soviet KGB for many years before beginning his political career, and has said the collapse of the Soviet Union was the "greatest geopolitical catastrophe" of the 20th century. 

Putin also stresses Russian ethnic and cultural influences in Ukraine as reasons why it should be part of Russia. That was a significant part of the justification Russia used when it illegally annexed the Crimea region of Ukraine in 2014. 

President Biden has warned there would be consequences for Russia if it invades Ukraine. But he also last week appeared to say that the U.S. might not respond forcefully to a "minor incursion" by Russia. That statement tipped off a wave of outrage both inside and outside the United States, followed by an effort by the White House to clean up the president's comments. 

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"I've been absolutely clear with President Putin. He has no misunderstanding, if any, any assembled Russian units move across the Ukrainian border, that is an invasion," Biden said, adding that this would "be met with severe and coordinated economic response that I've discussed in detail with our allies, as well as laid out very clearly for President Putin."

While NATO and the United States are fortifying allies, including the Baltics, it is not likely the western alliance will send troops into Ukraine itself, where they would be at risk of a potentially major military engagement with Russia. 

Fox News' Lucas Tomlinson, Jennifer Griffin, Tyler Olson, and The Associated Press contributed to this report.