SLAVIANSK - At least three people were killed in a gunfight in the early hours of Sunday near a Ukrainian city controlled by pro-Russian separatists, shaking an already fragile international accord that was designed to avert a wider conflict.The incident triggered a war of words between Moscow and Ukraine's western-backed government with each questioning the other's compliance with the agreement, brokered last week in Geneva, to end a crisis that has made Russia's ties with the West more fraught than at any time since the Cold War. The separatists said armed men from Ukraine's Right Sector nationalist group had attacked them. The Right Sector denied any role, saying Russian special forces were behind the clash.Failure of the Geneva agreement could bring more bloodshed in eastern Ukraine, but may also prompt the United States early next week to impose tougher sanctions on the Kremlin - with far-reaching potential consequences for many economies and for importers of Russian energy. The deal signed in Geneva last week by the European Union, Russia, Ukraine and the United States agreed that illegal armed groups would go home.So far, the pro-Russian militants have shown no signs of budging, though there was some hope of progress after Kiev said it would not move against the separatists over Easter, and international mediators headed to eastern Ukraine to try to persuade them to disarm. But the shootings near Slaviansk - already a flashpoint for tensions between Ukraine's rival camps - are likely to make that task even harder, hardening the view of pro-Russian sections of society that they cannot trust Kiev.‘The Easter truce has been violated,’ the Russian foreign ministry said in a statement. ‘This provocation - testifies to the lack of will on the part of the Kiev authorities to rein in and disarm nationalists and extremists.’ The town's self-appointed pro-Russia mayor placed a curfew on the town and appealed directly to Russia's Vladimir Putin to consider sending in peace-keeping troops. The Ukrainian foreign ministry hit back, reproaching Russia for hurrying to comment, without having the facts to hand to support its accusations.‘The Russian side must be reminded about their obligations under the Geneva agreement to bring all necessary influence to bear on separatists to clear illegally held buildings, unblock roads, lay down arms and prevent any bloodshed,’ a statement said. Right Sector spokesman Artem Skoropadsky said it was a ‘blasphemous provocation from Russia: blasphemous because it took place on a holy night for Christians, on Easter night. This was clearly carried out by Russian special forces.’Separatist militiamen near the eastern Ukrainian city of Slaviansk told Reuters four vehicles had approached their checkpoint at around 2:00 a.m. (2300 GMT) and opened fire.‘We had three dead, four wounded,’ one of the separatist fighters, called Vladimir, told Reuters at the checkpoint, where there were two burned-out jeeps. He said the separatists returned fire and killed two of the attackers, who he said were members of the nationalist movement which has its power base in the Ukrainian-speaking west of the country and is reviled by many in the Russian-speaking east. Police in Kiev said three people had been killed and three wounded.A Reuters cameraman at the scene said he saw the bodies of two people, one with what appeared to be gunshot wounds to the head and face, lying in the back of a truck. One of the dead was dressed in camouflage fatigues, the other, identified by several bystanders as a local man, was in civilian clothes. The deaths were the first in armed clashes in eastern Ukraine since the Geneva accord was signed on Thursday. Pro-Moscow rebels in the east Ukraine town of Slavyansk declared a curfew there Sunday, after a gun battle with unidentified attackers killed two militants. The self-styled separatist leader of the town, Vyacheslav Ponomaryov, told reporters that ‘the curfew comes into effect today - from midnight (2100 GMT) to 6:00am (0300 GMT),’ during which time it would be forbidden to be in the streets.