Unknown assailants on Friday threw Molotov cocktails and set alight the Kiev office of a Ukrainian judge overseeing the trial of two alleged Russian soldiers captured in the separate east.
The attack comes two weeks after police discovered the body of a Ukrainian lawyer who was brutally murdered after representing one of the two Russian suspects captured during a deadly May 2015 battle in the pro-Moscow region of Lugansk.
The incidents highlight the intense controversy and emotions the trial has stirred in both Russia and Ukraine.
Moscow argues that sergeant Aleksander Aleksandrov and captain Yevgeny Yerofeyev had delisted from the armed forces by the time they crossed the Ukrainian border, and were fighting alongside the insurgents by their own choice.
But the wounded men told foreign observers and reporters from their hospital beds in Kiev that they had been active members of Russia's GRU military intelligence service at the time.
They recanted their testimony once the court proceedings began.
Kiev police reported that the attack on Judge Mykola Didyk's office happened shortly after midnight.
"A group of young people climbed over a fence surrounding the Golosiyivsky court building and threw bottles with a flammable liquid" at Didyk's office, police said in a statement.
"According to the judge, documents relating to the criminal case (involving the two Russian suspects) were not damaged."
Police said they believed the attack was linked "to the judge's professional activities" but said no arrests had been made.
Military investigators have made some progress in the murder of Yuriy Grabovsky -- a Ukrainian attorney who went missing on March 5 and whose body was discovered buried in an abandoned farm with an explosive-packed bracelet around his leg on March 25.
One of two detained Ukrainian suspects has confessed to the murder and helped investigators locate Grabovsky's body.
But the motive of the killing remains unclear.
A new defence lawyer has been named to the case and the Russians' trial is set to resume later Friday.
Moscow angrily blamed the attorney's death on the "Russophobic hysteria" allegedly being fanned by Ukraine's pro-Western leadership.
Ukrainian President Petro Poroshenko has proposed swapping the soldiers for Nadiya Savchenko -- a Kiev-born helicopter pilot who was sentenced in Russia to 22 years in prison for her alleged involvement in the killing of two Moscow reporters in the war zone.
But such an exchange is complicated by Savchenko's continued denial of any wrongdoing. Russian law says that foreign convicts may only be sent home to serve their time there once they confess.
Savchenko began refusing all food and liquids in protest at her sentencing on Wednesday.