KYIV, Ukraine/WASHINGTON Jan 30 (Reuters) - The United States will not provide the F-16 fighter jets that Ukraine has sought in its fight against Russia, President Joe Biden said on Monday, as Russian forces claimed a series of incremental gains in the country's east.

The brief exchange came shortly after Ukrainian President Volodymyr Zelenskiy said that Russia had begun exacting its revenge for Ukraine's resistance to its invasion with relentless attacks in the east.

Pushilin's adviser, Yan Gagin, said fighters from Russian mercenary force Wagner had taken partial control of a supply road leading to Bakhmut, a city that has been Moscow's main focus for months.

That allowed Russia to apply pressure at Bakhmut and fortify the front against a future Ukrainian counter-attack, its researchers said in a report, though they said Ukraine could still recapture territory once the promised weapons arrive.

Russia's invasion, which it launched on Feb. 24 last year claiming it was necessary to protect itself from its neighbour's ties with the West, has killed tens of thousands of people and driven millions from their homes.

Additional reporting by Pavel Polityuk, Kevin Liffey, Ronald Popeski and Reuters bureaus; Writing by Peter Graff, Philippa Fletcher and Doina Chiacu; Editing by Gareth Jones, William Maclean and Cynthia Osterman