Moscow spent more than $1 billion supplying a separatist rebellion in east Ukraine and at least 220 Russian soldiers have been killed there, a report by Russian opposition activists said on Tuesday.

The report was the last project of murdered Kremlin critic Boris Nemtsov, who used open source information and interviews with families to paint a picture contradicting Moscow's argument that no serving Russian troops are fighting in Ukraine.

Nemtsov was shot dead in central Moscow in February and members of his party, the liberal RPR-Parnas, and several opposition journalists helped finish the 65-page report.

A spokesman for the Kremlin declined to comment on the report, saying he was not familiar with it and could not say if Russian President Vladimir Putin would look into it.

Ilya Yashin, who was an aide to Nemtsov, accused Putin of lying to Russians by waging the war amid denials of involvement.

“The war with Ukraine is an undeclared war, a vile cynical war which amounts to a crime against all of the Russian nation. Putin will go down in history as the president who made Russians and Ukrainians foes,” he told a news conference on the report.

The West accuses Russia of providing arms and troops to the separatists fighting government troops, as well as giving them training and intelligence. It stepped up sanctions on Moscow over the conflict, which has killed more than 6,100 people.

The West first imposed sanctions on Russian businessmen and officials after Moscow annexed Ukraine's Crimean Peninsula in March 2014, before unrest spread to the east of the country.

The report, which Nemtsov started after families of Russian troops killed in east Ukraine asked for his help, said at least 150 Russian servicemen were killed in fighting around the village of Ilovaisk and elsewhere in the region last summer.

Their relatives received about $60,000 in compensation provided they did not speak publicly about the deaths, according to the report.

Another surge in violence killed at least 70 Russian soldiers in clashes around the town of Debaltseve earlier this year, the report said, adding that the relatives of these troops were left without compensation.

Authors said Russian soldiers were mostly forced to quit the army officially before heading to east Ukraine, a move to support Moscow's argument that there are no serving Russian troops there, only volunteers.

They estimated that Russia spent more than $1 billion over 10 months to support Russian “volunteers” and local rebels as well as provide military equipment.

The report said Russians fighting against Kiev troops in east Ukraine earn up to $1,774 a month.

Reuters