and fighter jets were heard and seen. swooping over an airfield in east Ukraine.
Authorities say Ukrainian armed forces retook a military airfield from pro-Russian forces on Tuesday--
It was the first, formal military action by Ukraine against pro-Russian militants.
"The main purpose of these actions is to protect Ukrainian citizens, to stop terrorism, crime and the attempts to tear apart our country."
Witnesses say Ukrainian troops stepped out of military helicopters in a heavy pro-Russian area of Kramatorsk on Tuesday.
Despite gunfire, locals have not confirmed casualties as reported by Russian media.
Around the same time, a similar operation of Ukrainian army troops and special forces were deployed in a nearby city of Slavyansk to take back control of government buildings there.
Russia says Ukraine is on the brink of a civil war and has asked the United Nations to condemn Kiev's latest military operation.
However, the UN Secretary-General's press office said that Ban Ki-moon spoke on the phone with Russian President Vladimir Putin on Tuesday and requested all parties calm the situation.
"The Secretary-General is gravely concerned by the disturbances ongoing in eastern Ukraine. He has called on all parties to do their utmost to deescalate the situation and avoid further violence."
The U.S. also spoke out saying Ukraine's government has a responsibility to respond to "provocations" in its country but added Washington was not considering sending arms to Kiev.
Connie Lee, Arirang News.