MOSCOW (Reuters) - President Vladimir Putin said Russian forces have bolstered their positions across the entire front line in Ukraine after what he said was the failure of Ukraine's counteroffensive this year.

Putin's decision in 2022 to send tens of thousands of troops into Ukraine started a war which has left swathes of Ukraine devastated and hundreds of thousands of people dead or injured.

Russia currently controls about 17.5% of Ukrainian territory and a four-month-old Ukrainian counteroffensive this year by Ukrainian forces has made almost no net territorial gains, according to Western analyses of the territory held by Russia.

While Ukraine took back territory taken by Russia last year, the Ukrainian army has struggled to penetrate Russian lines which have been bolstered with mine fields and thousands of extra Russian troops.

"As for the counteroffensive, which is allegedly stalling, it has failed completely," Putin said in video remarks posted to social media by a Kremlin journalist Pavel Zarubin.

"The opposing side is preparing new active offensive operations. We see it and we know it," Putin said when asked about the battle for the eastern Ukrainian town of Avdiivka.

Both Russia and the United States have described the upsurge of fighting around Avdiivka as a new Russian offensive.

"What is happening now along the entire length of the [line of] contact is called 'an active defence'," Putin said. "And our troops are improving their position at almost the entire area. Quite a large area."

According to the Belfer Center at Harvard, Ukraine made a net gain of 8 square miles of territory the month to Oct. 10.

The conflict in eastern Ukraine began in 2014 after a pro-Russian president was toppled in Ukraine's Maidan Revolution and Russia annexed Crimea, with Russian-backed forces fighting Ukraine's armed forces.

(Writing by Lidia Kelly in Melbourne; editing by Guy Faulconbridge and David Evans)