Women gather to take part in a peace march in tribute to the victims onboard a passenger bus, which came under fire near the town of Volnovakha, January 18, 2015. [Photo/Agencies]

UNITED NATIONS -- UN Secretary-General Ban Ki-moon on Sunday called for an immediate and full cessation of hostilities in East Ukraine as violence escalate in the restive areas.

"The Secretary-General 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 cease-fire," said a statement issued here by Ban's spokesperson.

Ban stressed that further deterioration of a situation that has led to heavy loss of life and civilian suffering "must be avoided at all costs."

"He implores all sides to make good on their commitments under the Minsk Protocol and Memorandum, with the first step being an immediate and full cessation of hostilities," the statement said.

The UN chief added that the world organization stands ready to support all efforts toward de-escalation and the resumption of a genuine peace process to restore Ukraine's stability and territorial integrity.

Violence flared with new vigor in East Ukraine over the past week and casualties have mounted, including 13 civilians killed in an attack on a passenger bus in Donetsk.

On Sept. 5, 2014, a ceasefire protocol was signed in the Belarussian capital of Minsk between representatives from Kiev and the rebel leadership in an attempt to end the bloody conflict in East Ukraine, but the agreement has never been fully implemented.

According to UN figures, the violence in East Ukraine has already claimed more than 4,800 lives and displaced over one million people.