MOSCOW, Jumada II 25, 1435, Apr 25, 2014, SPA -- The chief of the Russian general staff voiced concern on Friday to the top U.S. military officer over the situation in southeastern Ukraine and the loss of life in a Ukrainian operation there this week, the Interfax news agency reported, according to Reuters. In a telephone call, Russian General Valery Gerasimov also told U.S. General Martin Dempsey that Ukraine had deployed a "substantial group of forces" near the Russian border, including troops whose purpose was to conduct sabotage, Interfax said. Ukrainian forces killed up to five pro-Moscow separatists on Thursday in an operation to regain control of areas held by rebels. -- SPA 22:07 LOCAL TIME 19:07 GMT www.spa.gov.sa/1225240