KYIV- Ukraine has collected 18 billion cubic meters (bcm) of gas in its underground storages and plans to increase the reserves to up to 20 bcm by the start of the 2021/22 heating season in mid-October, Prime Minister Denys Shmygal said on Wednesday.

Ukraine produces 65% of the gas it consumes and imports the rest from Europe.

The country used to buy gas from Russia but stopped in November 2015 after Kyiv's relations with Moscow soured over Russia's annexation of Crimea and the Kremlin's support for separatists in the eastern Donbass region.

Yuriy Vitrenko, the head of state energy firm Naftogaz, said last month additional volume of gas in reserves may be required to avoid shortages in winter due to problems with insufficient coal supply for thermal power generators.

Shmygal did not disclose the details of imports and the gas price at which Naftogaz will buy fuel.

He said the government would announce a competition to elect three independent directors to Naftogaz's supervisory board, which is due to end this fall.

Ukraine's government unexpectedly named Vitrenko, acting energy minister, as Naftogaz CEO in April, replacing Andriy Kobolyev, who had run Naftogaz for seven years.

The move prompted Western backers to warn that integrity and transparency in such appointments were key to maintaining confidence in Ukraine's commitment to reform.

In recent months, gas prices in Europe have reached record levels but Ukraine said that the rise in prices was artificial and caused by a decrease in Russian gas supplies to Europe.

(Reporting by Pavel Polityuk; Editing by Emelia Sithole-Matarise) ((pavel.polityuk@tr.com; +380 44 2449150; Reuters Messaging: pavel.polityuk.thomsonreuters.com@reuters.net))