Mariupol , Ukraine ( CNN ) Less than two days into a ceasefire in eastern Ukraine , deadly violence erupted once again between the military and pro-Russian separatists , casting further doubt about whether the peace plan will hold . Five Ukrainian security forces were killed and 25 were wounded in fighting with the separatists , Ukrainian defense spokesman Andriy Lysenko said . He said at least 129 violations of the ceasefire have already taken place -- ranging from small arms fire to mortar attacks . But pro-Russian separatists have also blamed Ukraine for violations . Dmytro Chalov , a spokesman for a sector of the Ukrainian army , said mortar fire pummeled the Mariupol area of eastern Ukraine . The ceasefire went into effect more than 24 hours earlier , at midnight Saturday night . Monday was slated to be a key day in the truce -- when both sides are supposed to withdraw heavy weapons . But neither has done so . The Ukrainian army still has plans to pull heavy weapons out of the area , but it wo n't happen until the situation is quiet , Chalov said . `` We emphasize that our military will only fire in response , '' Lysenko told reporters Monday . The ceasefire aims to end 10 months of fighting in eastern Ukraine . But less than 90 minutes after it started , Ukrainian officials reported mortar shelling at a military post near Zolote in the Luhansk region . Ukrainian President Petro Poroshenko has warned that if the separatists do not abide by the ceasefire , he will impose martial law throughout Ukraine . Despite the reports of violence Monday , the truce did appear to hold up in many parts of eastern Ukraine . And that means some residents who have been holed up for weeks were able to venture out to buy food and medicine . But the future remains uncertain . `` How long can this bloodshed go on for ? '' one woman told CNN . `` All we want is peace . '' Frederik Pleitgen reported from Mariupol , and Holly Yan wrote from Atlanta .
A Ukrainian defense spokesman reports 129 violations of the ceasefire so far . The rebels have been shelling government positions in Donetsk and Luhansk regions for several days now.