At least two people were killed Saturday in a gun and grenade attack in a western Ukraine city involving the country's notorious nationalist militia Right Sector.

Police had surrounded some gunmen in a wooded area of the city of Mukachevo and were trying to negotiate their peaceful surrender, a statement from the regional prosecutor's office said. But details of the violence remained confused.

The prosecutor's statement said about 20 armed people bearing Right Sector insignia surfaced in the early afternoon and called for a meeting with local residents at a cafe. They then began shooting, the statement said.

Ukrainian news reports earlier said that the violence broke out at a sports facility reportedly controlled by a national parliament member from a faction opposed to Right Sector. It wasn't clear whether the cafe referred to by the prosecutor statement was part of that facility.

The sports complex is connected to a national parliament member from a faction strongly opposed to Right Sector, said Anton Gerashchenko, an adviser to the Interior Ministry.

A Right Sector statement reported by Ukrainian news media said two of the militia's members had been killed. But Gerashchenko said three were killed and that three policemen and four civilians were wounded. He also said the attackers destroyed two police cars with grenade launchers.

The Right Sector statement said its members were attacked by "bandits" connected to Mikhail Lano, who reportedly controlled the sports facility, which local media said includes a gym and swimming pool.

Right Sector was one of the most militant factions in the massive protests in Ukraine's capital that led to pro-Russia President Viktor Yanukovych fleeing the country in February 2014. After war broke out in eastern Ukraine between government forces and pro-Russia separatists several months later, Right Sector has fought on the government side and Amnesty International has accused the group of holding civilians as prisoners and torturing them.

Right Sector leader Dmytro Yarosh holds a seat in parliament, but the group has little formal involvement in conventional politics. Russia has been harshly critical of Ukrainian leaders for not taking a firm stand against Right Sector, saying Kiev's apparent tolerance of the group suggests the government harbors fascist leanings.

The Russian foreign ministry's envoy for human rights, Konstantin Dolgov, seized on Saturday's events to renew the criticism.

"Right Sector has again shown its bandit face in Mukachevo. In Kiev, they don't want to break with neo-Nazis," he wrote on Twitter.

A member of Ukrainian President Petro Poroshenko's bloc, Irina Friz, meanwhile said on Facebook that "I don't exclude the presence of Russian traces in the incident ... as this region is in the zone of interest for Russian special services."

Mukachevo is in far western Ukraine, near the borders of Poland, Hungary and Slovakia.