At least six Ukrainian troops were killed and nine others wounded in attacks by pro-Russian separatists in eastern Ukraine over the past 24 hours, the Ukrainian military command said Monday.The statement on Facebook denounced the violation of a ceasefire agreed in September with the separatists launching 39 artillery and rocket attacks Sunday against government troops.In addition, according to the Ukrainian military, the separatist militias ambushed a police patrol in which three policemen were killed and five others wounded.The Ukrainian command said the pro-Russian militias fired Grad missiles at its troop positions northwest of the city of Lugansk.There were also attacks late Sunday with mortar, grenade launchers and small arms on Ukrainian troops at the Donetsk International Airport.Ukrainian artillery returned fire with high-precision weapons, according to unconfirmed reports, killing 23 and wounding 27 separatists.