(NewsNation) — A former U.S. Marine who died last week is believed to be the first American citizen killed while fighting in Ukraine. 

An undetermined number of Americans — many with military backgrounds — are thought to be in the country helping battle Russian forces.

Andrij Dobriansky, director of communications for the Ukrainian Congress Committee of America, weighed in on just how helpful these Americans are during an appearance Sunday on NewsNation’s “Prime.”

“I think for the most part, these people who had come over earlier, volunteering and wanting to fight, perhaps a little bit too gung ho, were weeded out,” he said. “Ukraine made it clear that (to volunteer), you do need to have military experience, you do need to be a trained fighter.”

Willy Joseph Cancel was killed Monday while working for a military contracting company that sent him to Ukraine, his mother, Rebecca Cabrera, told CNN. 

Relatives say the 22-year-old was killed alongside Ukrainian forces.

Individual Americans are fighting side-by-side, even though U.S. forces aren’t directly involved in fighting aside from sending military material, humanitarian aid and money.

“The United States does warn for no Americans to cross over” into combat zones, Dobriansky said. “They would rather not see American lives killed in that manner.”

Still, Russia’s invasion has given Ukraine’s embassy in Washington the task of fielding inquiries from thousands of Americans who want to help in the fight, and Ukraine is using the internet to recruit volunteers for a foreign force, the International Legion of Defense of Ukraine.

Dobriansky warns, “it is a very real situation … anywhere you are within Ukraine is a potential target for Russia.”

That includes the western Ukrainian city Lviv, where Hollywood actress Angelina Jolie made a surprise visit Saturday, according to Lviv Regional Governor Maksym Kozytskyy on Telegram.

“When a person like Angelina Jolie comes to Lviv, it’s not necessarily a light moment,” Dobriansky said. “Those people over there fully understand the magnitude of somebody coming over into an area that can be bombed at any moment.”

Jolie’s visit could be seen both as bringing attention to the plight of the Ukrainian cause and as a potential distraction.

“A third option is helpful to see people who are brave enough to come into Ukraine,” Dobriansky said. “And just tell them that the rest of the world cares.”

It was this third sentiment that Dobriansky experienced when he traveled to Ukraine.

He describes meeting people on the ground “wanting to see that Americans do want to come” and people who are interested in knowing what “we’re doing over on our side of the border.”

Jolie — who has been a United Nations special envoy for refugees since 2011 — had come to speak with displaced people, including children undergoing treatment for injuries suffered in a missile strike.

“What (Jolie) saw was people making the best of it in a very difficult situation,” Dobriansky said. “And to have somebody of Angelina Jolie’s magnitude come over there is very important for those people.”

According to Dobriansky, “That is the nature of this horrible war, the fact that no civilian is safe.”

“Anybody walking in there is a potential target,” he said, “simply because of the amount of rockets that come over from Russia.”

The Associated Press contributed to this report.