The United Nations said in a statement Sunday, that Ban Ki-moon "is alarmed by the severe escalation of fighting for control of Donetsk airport in eastern Ukraine, which has already caused numerous casualties and threatened to completely unravel a hard-won September 2014 ceasefire".
The UN Secretary General urged Kiev forces and independence fighters not to forget "their commitments under the Minsk Protocol and Memorandum, with the first step being an immediate and full cessation of hostilities" in southeastern Ukraine.
Fighting in southeastern Ukraine continues despite the ceasefire agreement reached between representatives of the self-proclaimed people's republics of Donetsk and Luhansk (DPR and LPR) and Kiev on September 5, 2014, in the Belarusian capital, Minsk.
Heavy weapons have not been withdrawn from the region, even though it was stipulated by a memorandum, signed at a meeting of the Contact Group on Ukraine in Minsk on September 19.
The city of Donetsk and the Donetsk airport have recently reemerged as a crisis area since the onset of the armed conflict in eastern Ukraine, where Kiev launched a military operation against local independence supporters in April.
According to UN estimates, more than 4,800 people have been killed in the course of the conflict since last spring.