Russian separatists in eastern Ukraine have asked Russia to send in troops after as many as three pro-Russian militants and one unknown gunman were killed in a shootout late last night. The shoot-out broke an Easter Sunday truce agreed upon by Ukrainian, Russian and American authorities.

The incident occurred at a roadway checkpoint outside the heavily pro-Russian city of Sloviansk. According to the pro-Russian militants stationed there, four vehicles pulled up to the checkpoint, refused to be checked and opened fire.

Russia and pro-Russians in Ukraine blame ultra-right-wing nationalists aligned with Kiev for the attack, prompting separatist leader  Vyacheslav Ponomaryov to call for Russian “peace-keepers” to protect them.

“Vladimir Vladimirovich (Putin), fascists who are killing our brothers are trying to conquer our small provincial town,” said Ponomaryov on Rossiya-24 News, “This is why we are asking you in the nearest time to consider the issue of introducing a peace-keeping contingent to protect civilians from the Right Sector and the national guard of Ukraine which bring about death.”

The Russian government said it was “outraged” by the incident and criticized the Ukrainian government for being “unwilling to put in check and disarm nationalists and extremists.”

President Putin told reporters on Thursday that he reserves the right to send troops into eastern Ukraine to protect the population there, but “very much hopes” he won’t have to. NATO estimates there are around 40,000 battle-ready Russian troops amassed on the Ukrainian border.

The Ukrainian government has denied any Ukrainian regulars or groups connected with the Ukrainian government were involved, going as far to call the incident a “cynical provocation” by the pro-Russian separatists orchestrated to justify Russian military intervention in the region.

A spokesman for Right Sector, the far-right nationalist group that took part in the Euromaidan movement and who pro-Russians blame for the attack, called the allegations “lies” and “propaganda” meant to discredit the transitional government in Kiev.

Pro-Russian militants in Sloviansk are now on alert after “People’s Mayor” Ponomarev told ITAR-TASS that the group has received word that an attack by far-right nationalists is “planned soon,” and they are preparing to defend themselves.