Donetsk airport is said to be of limited strategic value but is regarded as a symbolic prize of the conflict, with the army and rebels continuously battling for control.
The airport, once the pride of the city, has now been reduced to rubble.
Colonel Andriy Lysenko is Ukraine's military spokesperson.
"Yesterday, there was a decision made to relocate Ukrainian military personnel from the new terminal of Donetsk Airport. This building was completely destroyed and is not suitable for defence anymore. During combat, 16 soldiers were wounded and captured. Right now, negotiations are taking place in order to free them."
Earlier, mortar shells rained down on the center of Donetsk, killing at least 13 people at a bus stop.
It is far from clear who fired the mortars and each side accuses the other.
Alexander Hug, the spokesperson for the special monitoring Mission in Ukraine says the OSCE is trying to verify all the facts.
"Our verification at the moment is on-going. We have, as of now, seen seven bodies near the vehicle that has been hit. We have not concluded our fact finding and once we conclude, we will report so, publicly."
Ukraine's President, Petro Poroshenko, has called an emergency meeting to discuss a response to the escalating tension, which Kiev blames on Moscow, accusing the Kremlin of supporting the rebels.
Russia denies the accusation, and Foreign Minister Sergei Lavrov condemned the shelling of the bus in Donetsk as "a monstrous crime" whose ultimate responsibility rests with Kiev.
"We should not allow the party of war in Kiev - which is supported from outside and we know by who - to gain victory. We will do everything possible to stop this bloody and senseless conflict."
Thursday's violence came hours after the foreign ministers of Russia, Ukraine, Germany, and France ended a crisis meeting in Berlin with a joint call to cease hostilities.
No agreement on stopping the hostilities was reached.
The main achievement was that all sides agreed that the demarcation line agreed on in September would form the basis for the pull-back of heavy arms on both sides.
However, as the conflict escalates, that solution already looks doomed.
In light of the worsening situation in Ukraine, the European Union announced that it will step up humanitarian aid to needed people there.
The Chinese side has also issued a statement, urging for a lasting ceasefire deal to be reached as soon as possible.
For CRI, I'm Qi Zhi.
