Trevor Reed, the former US Marine who was detained in Russia before being freed in a prisoner swap last year, has been injured while fighting in Ukraine, the State Department said.
“Mr Reed was not engaged in any activities on behalf of the US government,” State Department spokesman Vedant Patel said.
Mr Patel said that he was not aware the government even knew of Mr Reed's plans to visit Ukraine.
He said Mr Reed was taken to Germany for medical care with the help of a non-government group.
The State Department has repeatedly warned Americans not to travel to Ukraine or take part in the fighting.
“We are not in a place to provide assistance to evacuate private US citizens from Ukraine, including those Americans who may decide to travel to Ukraine to participate in that ongoing war,” Mr Patel said.
The State Department has listed Ukraine as a “do not travel” country.
It warns of reports of Russian forces singling out US citizens in Russian-occupied areas of Ukraine for detention, interrogation or harassment.
“We have been incredibly clear that travelling to Ukraine, choosing to participate in the fighting there, has a very real risk of capture, of death, of bodily harm, and that continues to be our assessment,” Mr Patel said.
Mr Reed spent nearly three years in a Russian prison after being convicted in 2019 of endangering two officers while intoxicated on a visit to Moscow.
The US called his trial a “theatre of the absurd” and deemed him to be wrongfully imprisoned.
He was freed in April 2022 in a high-profile prisoner swap that saw the US hand over Russian pilot Konstantin Yaroshenko, who was jailed in the US on drug smuggling charges.
The release took place amid tension between the US and Russia over the war in Ukraine.
Watch former US marine Trevor Reed being escorted to a plane
Mr Reed was one of several US citizens held in Russia.
In December, US basketball start Brittney Griner was released from Russian custody in exchange for arms dealer Viktor Bout.
There are still at least two US citizens considered by Washington to be wrongfully imprisoned in Russia.
They are another former Marine, Paul Whelan, who has been held since 2018, and Evan Gershkovich, a Wall Street Journal reporter who was arrested on espionage charges in March 2023.
Since his release, Mr Reed has been a vocal supporter of other Americans detained abroad, calling on the US government to do more to help those held wrongfully in other countries.
Reuters contributed to this report
