"Unfortunately, the veteran's health is not the best, but he is ready to fight against Latvia to the end, even if that means to the end of his life," lawyer Mikhail Ioffe said at a news conference.
Vasily Kononov, 86, led a group of resistance fighters against Nazi Germany in the Baltic state during World War II. He was convicted by a Latvian court of ordering the killing of nine villagers in 1944, with some reports saying the dead included a pregnant woman.
He admitted to the killings, but said the dead were Nazi collaborators who were caught in crossfire. Latvia was under German occupation at the time of the incident.
The European Court of Human Rights last week accepted Latvia's appeal against a June ruling that Riga must pay the World War II veteran 30,000 euros ($47,000) in damages, now to be reviewed in the Strasburg court's Grand Chamber, the tvnet.lv website said.
The Latvian government filed the appeal after a June 19, 2008, ruling ordered Latvia to pay Kononov compensation for being held in custody on charges of war crimes.
Ioffe could not say when the hearing before the Grand Chamber would take place, but expressed the hope it would occur while Kononov was still alive.
Kononov had originally demanded 5 million euros ($7.8 million) in compensation and called the 30,000-euro award "a mockery." In 2007, the European court dismissed all charges against Kononov and declared him not guilty.
A retired police colonel born in Latvia, Kononov was arrested in 1998 and sentenced to six years in prison in 2000 on genocide charges. In 2004, after several years of litigation, his sentence was cut to 20 months and the charges changed to "war crimes." Kononov filed an appeal with the Strasbourg court the same year.
The court rejected Kononov's other demands, which included moral damages and compensation for the apartment and plot of land he had been forced to sell in order to pay for court expenses and medical treatment.
Russia subsequently applied pressure on Latvian and European authorities over the case and in April 2004 Kononov was granted Russian citizenship by then-President Vladimir Putin.