Separatist rebels and government troops have both reported violations of a ceasefire that was supposed to begin in eastern Ukraine at midnight.
Rebels on Tuesday declared a unilateral ceasefire, and visiting German foreign minister Frank-Walter Steinmeier (pictured) said the following day that Ukraine had agreed to observe the truce.
Russian state television has quoted rebel officials as saying their forces came under mortar fire.
Ukrainian army spokesman Ivan Arefyev said fighting subsided at midnight but rebels used small arms and hand grenades in the morning, the Interfax news agency said.
The foreign ministers of France and Germany, key mediators in the Ukrainian peace process, met the Ukrainian president on Wednesday and are expected to travel to the east on Thursday.