The Ukrainian army on Saturday reported 11 attacks against its positions in the east where a ceasefire is tentatively holding and said a drone was spotted over Mariupol, the last major eastern town under its control.
"The surveillance activities of the enemy have intensified around Mariupol where a drone was identified," the military said in a statement.
Ukraine has been worried for months that the Russia-backed separatists will launch an offensive on Mariupol in a bid to build a corridor between the Russian border and the Crimean peninsula, which was annexed by Moscow in March.
The ceasefire introduced on Tuesday was violated 11 times in the past 24 hours, the statement said, with artillery and mortar fire reported at several flashpoints along the line.
Around the airport in Donetsk -- site of some of the fiercest fighting between government and separatist forces in recent months -- "the night was rough", a voluntary soldier, Maxim, with the right-wing Pravy Sektor group told AFP.
"Snipers fired on us and explosions were coming from the airport. But everything is calm this morning," he said.
Volodymyr Tiurin, an official in a town in the neighbouring Lugansk province, said all was calm.
"People slept soundly for the fourth night in a row," he said.
The ceasefire -- the fourth since the conflict broke out in April -- aims to bring an end to fighting that has claimed more than 4,300 lives and displaced nearly a million people.
At least five Ukrainian soldiers have been killed since it began, but clashes have greatly reduced.
The government has been pushing for a fresh round of peace talks, but the rebels have apparently been reluctant to take part.