Three nongovernmental organizations announced on Monday they had filed a landmark legal case in Moscow over the torture of a Syrian detainee.

The case against the Russian mercenary group Wagner comes after several cases in Europe seeking justice for torture victims in the Syrian war. 

"This litigation is a first-ever attempt by the family of a Syrian victim to hold Russian suspects accountable for serious crimes committed in Syria," the International Federation for Human Rights (FIDH), the Syrian Center for Media and Freedom of Expression (SCM) and Russian rights group Memorial said in a joint statement.

What is the case?

The three NGOs said they filed the case on behalf of a family member of a Syrian torture victim.  

The victim was "tortured, killed, and had his corpse mutilated by six individuals in 2017," the NGOs said in a statement. 

They accuse the Kremlin of using Wagner fighters to evade accountability for human rights violations committed in Syria.

What is the Wagner group?

Since 2014, rights groups and media reports have linked the private military group to separatist insurrection in eastern Ukraine, and bolstering conflicts in Libya and the Central African Republic. 

The group allegedly reels in law enforcement and military soldiers with salaries at least five times higher than their average income in Russia, according to the AFP news agency. 

Russian businessman Yevgeny Prigozhin is believed to finance the group. The European Union and the United States previously imposed sanctions on Prigozhin over meddling in Libya's conflict and US elections. 

The 59-year-old is said to have close ties to Russian President Vladimir Putin and is dubbed "Putin's chef" by the media. He denies links to the Wagner group. 

Rights groups have long slammed Russia for its involvement in the Syrian war, accusing the Kremlin of targeting civilians.