The Organization for Security and Co-operation in Europe (OSCE) reported more than 200 ceasefire violations in eastern Ukraine in a single day, the DPA reported on Saturday.
The OSCE is monitoring the conflict between Ukrainian government forces and Russian-backed separatists in the Donetsk and Lugansk areas.
Earlier this week, under the mediation of France and Germany, the parties agreed to re-engage in a ceasefire reached a year and a half ago but then repeatedly violated.
The OSCE monitoring mission reported 173 ceasefire violations, including 156 explosions in Donetsk. There were 84 ceasefire violations, including 45 explosions in Lugansk. Data refer to Thursday.
The Ukrainian army said on Saturday morning that the separatists had violated the ceasefire five times the previous day and that one soldier had been wounded.
The violations suggest that the conflict that erupted in 2014 is not calming down, despite the latest diplomatic effort.
The United Nations estimates that more than 13,000 people have died so far.
For several weeks, reports of alleged Russian preparations for an armed invasion of Ukraine have caused concern. Russia has denied planning for such actions.
According to the Interfax agency, the Russian army announced on Saturday that 1,000 soldiers with tanks and helicopters carried out maneuvers near Voronezh, on the border with Ukraine, informs Agerpres.