John Harding, Andrew Hill and Dylan Healy have been accused of being mercenaries and “undergoing training to seize power by force,” according to Russian media.
The other two captured men are Matthias Gustafsson from Sweden and Vjekoslav Prebeg from Croatia.
On Monday, all five appeared in court and, if found guilty, they could face the death penalty under the laws of the self-proclaimed Donetsk People’s Republic (DPR).
Russian state-owned news agency TASS reported: “Asked by the judge if the charges were clear to them, all defendants answered in the affirmative but pleaded not guilty.
“Four defendants agreed to testify and the fifth, British citizen John Harding, refused.”
The next court hearing in their case is scheduled for October, the Interfax news agency reported, citing a statement by the separatists’ court.
Ahead of the trial earlier this week, US secretary of state Antony Blinken tweeted: “We are concerned by reports of British, Swedish & Croatian nationals being charged by illegitimate authorities in eastern Ukraine.
“Russia and its proxies have an obligation to respect international humanitarian law, including the rights & protections afforded to prisoners of war.”
On 9 June, the DPR’s supreme court sentenced two Britons, Aiden Aslin and Shaun Pinner, and Moroccan national Brahim Saadoun, to death for the same charge of mercenarism. All three have appealed their verdicts.
The Ministry of Foreign Affairs of Ukraine said the so-called judicial process against the men was “worthless”.
Oleh Nikolenko, spokesman for the ministry, said on the day that the two Britons and the Moroccan were sentenced to death: “All foreigners who fight on Ukrainian territory as part of the Armed Forces of Ukraine are members of the Armed Forces of Ukraine.
“According to international humanitarian law, they are subject to the legal status of combatants.”