A Chinese newspaper with close ties to the ruling Communist Party on Monday condemned the assassination of Russian opposition leader Boris Nemtsov, saying it severely damaged that country's body politic.

"This incident has dealt a heavy blow to Russia's national unity and added pressure to the Russian government in dealing with thorny issues," the Global Times tabloid said in an editorial.

Nemtsov, a 55-year-old anti-corruption crusader, government critic and deputy premier in the 1990s under Boris Yeltsin, was shot in the back shortly before midnight Friday near the Kremlin, sparking anti-government protests.

The delicately worded Global Times editorial, in parts fiercely critical of the killing while in others sympathetic to Moscow, reflected Beijing's position as an ally of Russia. President Vladimir Putin has a close relationship with Chinese leader Xi Jinping.

"The murder of Nemtsov runs counter to common political logic and people feel odd about it," the editorial said, while careful to stress that Putin had condemned the killing even as it mentioned Western media reports "implying that Putin was behind this murder".

"Chinese society is eager to see a stable Russia under Putin's reign and is shocked to see such cruel behaviour in Moscow," said the paper, which is affiliated to the People's Daily newspaper, the ruling Communist Party mouthpiece.

"We hope it is just an isolated case and not as grievous as has been depicted in the Western discourse."

Separately, Chinese foreign ministry spokeswoman Hua Chunying said Beijing "strongly condemns" the assassination.

It was a "domestic matter" for Russia, she told a regular briefing.

Asked whether China was concerned the killing could lead to political instability harmful to Beijing-Moscow relations, she expressed confidence that Russian authorities would "maintain their domestic stability".

The Global Times editorial also condemned political assassination in general, calling it "the most shameful act" and "an outdated strategy" seldom used in civilised society.

"Assassination of opposition leaders is especially senseless because the outrage triggered by such an act can only enhance cohesion of the opposition, rather than weakening it."

High-ranking Chinese Communists who have fallen from favour have sometimes met untimely ends, and Beijing last year expressed sympathy for a Korean national hero's 1909 killing of a Japanese official on Chinese soil.