(NewsNation) —Three U.S. citizens who went to Ukraine to aid in its war effort are being held captive by Russia, adding a new wrinkle to the relationship between Washington, D.C., and Moscow during what experts are calling a pivotal moment in the war.

The U.S. government has been warning Americans not to travel to Ukraine since the Russian invasion of the sovereign nation began in February, citing the extreme risks that come with traveling to a war zone, particularly one where Russia is a combatant.

Alexander Drueke, 39, of Tuscaloosa, Alabama, U.S. Marine veteran Grady Kurpasi and Andy Huynh, 27, of Hartselle, Alabama, are believed to be the three captured Americans.

Those warnings, however, did not stop some U.S. citizens from traveling to Ukraine to fight or offer aid. Retired Air Force Lt. Gen. Richard Newton said on “NewsNation Prime” it is still critical Americans do not travel to Ukraine for any reason, as it likely will only serve to “significantly complicate” the war effort.

“There’s other things Americans can do to help the cause of the Ukrainian government, and the people for that matter,” Newton said. “There’s nongovernmental organizations, there’s helping with food relief and so-forth, things you can even do behind the lines outside of Ukraine.”

Newton said having captured Americans in Ukraine will only further strain an already extremely tense relationship between the Vladimir Putin regime and Washington.

“Something that is happening tactically on the battlefield, if these Americans have indeed been captured, now raises it really to the strategic level,” Newton said. “Now you’ve got issues going on between capitals, between Washington, D.C., and Moscow.”

The reported capture of Americans by Russian forces comes at a time when Ukraine is suffering heavy losses fighting in the eastern Donbas region, where Russia is attempting to put a stranglehold on the region.

Ukrainian President Volodymyr Zelenskyy visited the front line in the Odesa region this week and also secured more aid in the form of military training from the European Union. Still, Zelenskyy has been calling for more weapons to be delivered to his troops by allies as the bloody war drags on.

Captured American only complicate all of those matters, Newton said.

“It really does complicate our position there at a time when the conflict is at a really culminating point,” Newton said. “Russia is really starting to hold its ground in the east and Ukraine is trying to figure out how it can take the Donbas area. So it’s just really bad timing.”

Newton said his heart and mind go out to the families of the captured Americans, but added traveling to Ukraine only “unnecessarily” adds to an already troubling situation.

“The current situation with the fight going on between Ukraine and Russia is getting much more complex, it’s getting much more engaged with heavy artillery … and so we just don’t need freedom fighters over there getting in the middle of all that,” Newton said.