MSNBC Contributor Malcolm Nance Joined International Force Fighting Russia in Ukraine: 'Done Talking'

Malcolm Nance/Twitter

As he has many times before, terrorism and intelligence analyst Malcolm Nance appeared on MSNBC's The ReidOut on Monday. But for his latest interview with host Joy Reid, he donned fatigues and revealed that he had joined Ukraine's fight against Russia — out of a sense of duty, despite the dangers and the stern warnings from the U.S. government.

"I'm DONE talking," Nance, 61, wrote Monday in a tweet that shows him holding up a weapon.

The author, executive director of a counterterrorism think tank and former U.S. Navy senior chief petty officer told Reid that hearing from friends under fire in eastern Ukraine convinced him to join the International Legion of Territorial Defense of Ukraine, which reportedly includes more than 20,000 foreign volunteers from 52 countries.

"I am here to help this country fight what is essentially a war of extermination," Nance said on The ReidOut. "This is an existential war, and Russia has brought it to these people and is mass murdering civilians."

RELATED: Regardless of the Warnings, Some U.S. Veterans Look to Join the Fight in Ukraine: 'This Is What I Do'

Though Russia has denied targeting civilians in its invasion of Ukraine, thousands of casualties, including of children, have been reported across the country.

U.S. President Joe Biden has called Russian leader Vladimir Putin, who ordered the attack in late February, a "war criminal" and accused Russians of genocide.

"We are here for one purpose and one purpose only and that is to protect the innocent people of Ukraine from this Russian aggression," Nance, who said he joined the fight about a month ago, said on Monday.

"It's not a conventional war," he continued, saying that Russians were "using mass heavy weapons that are used in combat against civilians. They are destroying infrastructure and then you find that they go to the cities and massacre men, women and children."

Nance is not alone in heading to a fight on foreign soil.

Hundreds of Americans previously contacted Ukraine's embassy in Washington, D.C., answering a call from Ukraine's foreign minister who initially solicited volunteers after Russia began its invasion.

"Foreigners willing to defend Ukraine and world order as part of the International Legion of Territorial Defense of Ukraine, I invite you to contact foreign diplomatic missions of Ukraine in your respective countries," the minister wrote on Twitter. "Together we defeated Hitler, and we will defeat Putin, too."

The U.S. State Department, however, is not eager for any U.S. citizens to travel to Ukraine to engage in combat — which could lead to them being captured, killed or used for political propaganda purposes or recruited and radicalized by other groups, officials have warned.

RELATED: Canadian Sniper Among Foreigners Joining Ukraine in Fight Against Russia — 'I Want to Help'

In an advisory posted to its website, the department said that although it was "not a crime under U.S. law for an individual to go abroad for the purpose of enlisting in a foreign army," it could be a violation if that person was recruited or hired in America — and could even be grounds for "the relinquishment of U.S. citizenship."

State Department spokesman Ned Price warned in March that beyond the obvious risks to personal safety, "U.S. citizens should be aware that Russia has stated that it intends to treat foreign fighters in Ukraine as 'mercenaries,' rather than as lawful combatants or prisoners of war."

Nance, however, said on Monday that he's not worried about being singled out by Russian troops.

"The war that's being waged here is being waged against everybody," he told Reid. "They're not going around hunting for American flag patches or to see who's Black, who's Asian, who's Latino. We are part of the Ukrainian armed forces. We are brothers and sisters with the Ukrainian army … We are fighting side by side, elbow to elbow with them … They are grateful for the help and I'm grateful to be here."

Sipa via AP Images Ukrainian civilian volunteers and reservists of the Kyiv Territorial Defense unit conduct weekly combat training in an abandoned asphalt factory on the outskirts of the capital.

RELATED: Businessman Dad-of-2 Trained as a Sniper to Defend Ukraine — Now He Talks Life in the Resistance

Meanwhile, Russia's attack on Ukraine continues after nearly two months.

Details of the fighting change by the day and the actual number of deaths is difficult to determine.

More than 4 million have fled the country as refugees — and half are children, according to the United Nations. Millions more have been displaced inside Ukraine.

The invasion, ordered by Putin, has drawn condemnation around the world and increasingly severe economic sanctions against Russia.

With NATO forces amassed in the region, various countries are offering aid or military support to the resistance. Ukraine's President Volodymyr Zelenskyy has called for peace talks — so far unsuccessful — while urging his country to fight back.

Putin insists Ukraine has historic ties to Russia and he is acting in the best security interests of his country. Zelenskyy vowed not to bend.

"Nobody is going to break us, we're strong, we're Ukrainians," he told the European Union in a speech in the early days of the fighting, adding, "Life will win over death. And light will win over darkness."

The Russian attack on Ukraine is an evolving story, with information changing quickly. Follow PEOPLE's complete coverage of the war here, including stories from citizens on the ground and ways to help.