Ukraine has reopened two of the three airports, Kharkiv and Dnipropetrovsk, that had been shut down from 13 December due to security reasons.
The airports had been closed at a request by Ukraine's State Aviation Service as the country's security service launched 'anti-terror operations' there, the Ukrainian online publication Apostrof reported.
"While flights have started operations from the Dnipropetrovsk Airport since Tuesday, a flight ban will continue at Zaporizhia airport until Saturday," said Denis Antonyuk, head of Ukraine's State Aviation Service.
A statement from the state aviation service said: "The airspace over Dnipropetrovsk and Kharkiv airports is open from 9pm 15 December. All flights have resumed. The closure of airspace over the airport in Zaporizhya is prolonged till 6am on 20 December."
TASS quoted Antonyuk as saying: "We decided to secure ourselves and extended the flight ban at Zaporizhia Airport until Saturday."
It was further reported that the closure came after reports in the Russian media that said that US C-130 Hercules transport planes were unloaded at Zaporizhia Airport, which led to the airport's perimeter to be reinforced by the hasty erection of defensive towers.
However, The Interpreter reported that Ukraine's National Security and Defense Council (NSDC) officials said they had no information about why Gosaviasluzhba, the state air service, was closing the airports in the three cities. At a briefing, spokesman Andrey Lysenko said the reasons were not known, and that the decision was up to the company managing the air traffic.
Ukraine had previously disrupted air links from its eastern city of Donetsk since May. The country has also banned flights between Kharkiv and Moscow in May, and between Dnipropetrovsk and Moscow in December.