(Reuters) - Russian forces have firmed their positions in the Strilecha-Lyptsi area of Ukraine's Kharkiv region, keeping under fire control Ukraine's defence line, a Moscow-installed official in Kharkiv said on Friday.

"The control of strategic hills nearby the settlement of Lyptsi allows our troops to keep under fire control the immediately adjacent defence line to the city of Kharkiv, and control all supply routes," Vitaly Ganchev, a Russian-installed official in Kharkiv told Russia's RIA state news agency.

That includes the Strilecha-Lyptsi area between two small villages and the vicinity of the border town of Vovchansk where there has been street fighting.

On Thursday, Ukraine's top commander said that Russia is building up forces near the northern part of Ukraine's Kharkiv region, but it still lacks the troop numbers to stage a major push in the area.

Russia opened a new front in the Ukraine war by pushing swiftly over the border into the Kharkiv region of northeastern Ukraine in early May with small groups of highly mobile units, a move that has forced Ukraine to rush in troops from other areas.

Ganchev told RIA that Russian forces have taken about 13 settlements in Kharkiv in May and about 300 square km (116 square miles) of land.

Reuters could not independently verify Ganchev's claims.

Ukraine's General Staff said on Thursday its forces were continuing to strengthen their defensive lines in the area and repelled one Russian attack near the village of Starytsia on the Kharkiv front.

(Reporting by Lidia Kelly in Melbourne; Editing by Christian Schmollinger)