By Tom Balmforth and Jonathan Landay

LONDON/WASHINGTON Aug 15 (Reuters) - Russia is preparing to test its new nuclear-capable, nuclear-powered cruise missile and if successful, plans to use the results to bolster its negotiating position with the West, Ukrainian military intelligence said on Friday.

Andriy Yusov, a spokesperson for the service, issued the written statement to Reuters just before U.S. President Donald Trump was due to hold talks in Alaska with Russian President Vladimir Putin on ending Moscow's war in Ukraine.

He did not give an assessment of the possible timing of the test in the statement, given in response to questions submitted by Reuters for a report published on Tuesday that Moscow was preparing to test the 9M730 Burevestnik cruise missile.

He did not say how his service arrived at its assessment. It has for years received intelligence from the United States and its NATO allies, and it has its own networks inside Russia.

Reuters on Tuesday reported two U.S. researchers and a Western security source as saying that Moscow was readying a test of the Burevestnik at its Pankovo test site on the Barents Sea archipelago of Novaya Zemlya.

The researchers said imagery from Planet Labs, a commercial satellite firm, showed extensive activities at the site, increases in personnel and equipment and the presence of ships and aircraft associated with previous tests of the weapon dubbed the SSC-X-9 Skyfall by NATO.

The Russian defense ministry, the Pentagon and the CIA declined to comment for that report. The White House did not comment directly on whether a test was being prepared, saying in response to a question about it that Trump wanted peace in Ukraine.

Yusov said Moscow, which has threatened to use nuclear weapons over the Ukraine war, saw a test as diplomatic leverage.

"Russia is preparing for another round of tests of the 9M730 Burevestnik," his statement said. "The purpose of these tests is to validate scientific and technical solutions implemented by the missile."

"If successful, Russia will leverage the test results to defend its interests in negotiations with the West," he continued.

Putin has said the weapon is "invincible" to missile defenses, with an almost unlimited range and unpredictable flight path.

But many experts say it is unclear if the missile can evade defenses, would not give Moscow capabilities it does not already have, and would spew radiation.

The Burevestnik has a poor test record, according to the Nuclear Threat Initiative advocacy group, with two partial successes among 13 known tests.

(Reporting by Jonathan Landay and Tom Balmforth; editing by Philippa Fletcher)

((Jonathan.Landay@thomsonreuters.com; +1 202-354-5885;))