By Edith Honan UNITED NATIONS, Oct 11 (Reuters) - Georgian security forces who fired on separatist fighters during a clash last month in the breakaway province of Abkhazia should be punished, Russia's United Nations envoy said on Thursday. "We demand that the organizers and persecutors of this criminal act be punished and that the Abkhazian soldiers who were captured be released," Ambassador Vitaly Churkin told a U.N. news conference. Russia has said Georgian forces attacked a training exercise to stoke tensions between Moscow and the former Soviet republic. A preliminary report by the U.N. Observer Mission in Georgia said that the Sept. 20 incident occurred 300 meters (yards) inside Abkhaz-controlled territory, which is consistent with Churkin's version of events. A spokesman for Georgia's U.N. mission was not immediately available for comment, but the report quoted Georgian officials as saying the separatists were planning to disrupt road construction and Georgian authorities intercepted them after crossing into Georgian territory. The U.N. also found that two former Russian officers "reportedly in contract with the Abkhaz de facto border guards" were killed in the incident, and that seven Abkhaz personnel were taken prisoner and several more were wounded. Autopsies of the former officers revealed they had been fired on at "point-blank range" with automatic weapons, the report said. "There is sufficient evidence to indicate that that was a gang-style execution. That, in fact, there is sufficient information that the Abkhazians did not return fire at all," said Churkin, citing the U.N. report. Relations between Tbilisi and Russia have soured over Moscow's support for Abkhazia and another breakaway region called South Ossetia. Tbilisi lost control over the regions in wars in the 1990s. The Security Council will discuss a further six-month extension to the mandate of the U.N. mission in Abkhazia on Oct. 15.