Timothy Griffin of New York killed fighting Russians in Ukraine

LONDON — Another U.S. citizen has died fighting in Ukraine, two people with knowledge of his death told NBC News on Monday, bringing the number of Americans killed in Russia’s war to at least six.

Timothy Griffin had been fighting alongside Ukrainians in the International Legion, which is made up of thousands of foreigners who have volunteered to help defend against the invasion, a spokeswoman for the division of Ukraine’s military told NBC News exclusively when approached for confirmation.

Griffin had been taking part in Ukraine’s counteroffensive on the eastern front, according to the International Legion. The legion’s spokeswoman said Griffin’s unit was conducting operations and came under attack, and he was “killed in action,” said the spokeswoman, who, under Ukrainian military protocol, declined to be identified other than by their callsign "Mockingjay.”

“We are in contact with the family and the International Legion and the Armed Forces of Ukraine are handling the repatriation process, in coordination with the family, following their wishes and instructions,” the spokeswoman said.

The legion declined to provide more details, including Griffin’s age, citing operational security and privacy concerns. But two people with knowledge of Griffin’s death said that he was from New York state and had fought in the Kharkiv region.

“Timothy’s memory will live on in his unit, in the Legion and the Armed Forces of Ukraine,” the International Legion said, adding that it was asking that the family’s privacy "be respected in this difficult time.”

A spokesman for the U.S. Embassy in Kyiv didn’t immediately respond to a request for comment.

In Washington, the State Department said it was “aware of these unconfirmed reports” of a U.S. citizen killed in Ukraine but that “due to privacy considerations, we have no further comment at this time.”

“We once again reiterate our message that U.S. citizens should not travel to Ukraine due to the active armed conflict,” a State Department spokeswoman said. “U.S. citizens in Ukraine should depart immediately if it is safe to do so using any commercial or other privately available ground transportation options.”

Ukrainian President Volodymyr Zelenskyy launched the International Legion, also known as the “foreign legion,” in the first week of the war in February, urging foreign citizens who are “friends of peace and democracy” to come to Ukraine to defend Western values that he said were larger than just Ukraine.

It’s unclear exactly how many Americans have traveled to Ukraine to fight. Ukraine’s foreign minister has said that roughly 20,000 foreigners overall have joined the effort.

Although the U.S. government has insisted it will not send U.S. troops to fight Russia on the ground in Ukraine, the number of Americans killed after traveling to fight there on their own volition has slowly increased.

In April, Willy Cancel, 22, who was working with a private military contractor, was killed in Ukraine, in what is believed to be the first death of a U.S. citizen fighting in the conflict. He was survived by his wife and their child, who was 7 months old at the time.

The next month, 52-year-old Stephen Zabielski of Hernando, Florida, was killed fighting in the village of Dorozhniank. And in July, the State Department confirmed that two more Americans had been killed in eastern Ukraine. They were later identified as Bryan Young and Luke Lucyszyn.

Last week, the body of a fifth American killed in Ukraine, 24-year-old Joshua Jones, was returned by Russia to Ukrainian custody. The Ukrainians are holding his body as part of a war crimes investigation, Jones’ family has said.

This article was originally published on NBCNews.com