UN Secretary-General Ban Ki-moon voiced alarm over fierce fighting around the Donetsk airport in eastern Ukraine and called for an immediate end to the violence.
Heavy shelling rocked the city as Ukraine rushed tanks to the front lines and declared it had pushed back pro-Russian rebels from most of the airport.
Ban on Sunday said in a statement that he was “alarmed by the severe escalation of fighting.”
The fighting threatened to completely unravel a September 2014 ceasefire, the UN chief said, calling for “an immediate and full cessation of hostilities.”
At least 14 people were killed, including four Ukrainian soldiers in fighting over the weekend. Houses were destroyed and electricity was cut for many homes and businesses as explosions repeatedly ripped through parts of the Donetsk region.
The United Nations stands ready to support efforts toward de-escalation, said Ban.
The Security Council is due to discuss the worsening crisis in Ukraine at a meeting on Wednesday, requested by Lithuania.
The conflict between pro-Russian rebels and Kiev government forces has killed more than 4,800 people since April last year and has become Europe’s worst humanitarian crisis since the Balkan wars of the 1990s.