The statement came hours before a government official said Tuesday that Ukraine's Defence Minister Andriy Taran had resigned -- reportedly on health grounds.

Taran, who had led the ministry since March 2020, has not commented on his resignation, a decision which parliament must ratify amid reports of an impending wider cabinet reshuffle.

The 66-year-old Taran "has complaints about his health", the leader of President Volodymyr Zelensky's faction in parliament, Davyd Arakhamiia, told reporters.

Opponents had criticised him during his tenure, citing insufficient reform of an under-resourced military.

Social media videos in recent days have shown Russian military trains and truck convoys moving tanks and missiles in the country's southwest near the Ukrainian border.

Pentagon spokesman John Kirby told reporters Monday that Washington was monitoring the situation, and The Washington Post quoted US officials saying they were concerned.

But Ukraine's defence ministry said in a statement late Monday that "no additional deployment" of Russian forces had been observed.

The videos could comprise "special informational and psychological actions" and show a planned troop movement after a Russian military exercise, it added.

- Zelensky-Biden talks -

Ukrainian President Volodymyr Zelensky said Tuesday he had discussed the conflict with US President Joe Biden on the sidelines of the COP26 climate conference in Glasgow.

"The US continues to support territorial integrity and reforms in Ukraine," Zelensky tweeted.

Zelensky also had a more formal meeting in Glasgow with Secretary of State Antony Blinken, who "reaffirmed the United States' unwavering support for Ukraine's sovereignty, independence and territorial integrity," a State Department statement said.

Kremlin spokesman Dmitry Peskov on Tuesday dismissed the reports of a potential build-up, saying there was no need to "waste time" on "low-quality" claims.

"The movement of our military equipment and army units... is exclusively our business," he told reporters. "Russia has never threatened anyone."

The Ukrainian army is locked in a simmering conflict with pro-Russian separatists that erupted after Moscow annexed Crimea in 2014.

After a rise in violence early this year, Russia in March amassed around 100,000 troops on Ukraine's borders, sparking fears of a major escalation.

Under pressure from Kiev's Western allies, Moscow later announced a pullback, but both Ukraine and the United States said at the time the withdrawal was limited.

Ukraine's military said Tuesday one of its soldiers had been killed in a separatist attack.

The conflict has claimed more than 13,000 lives to date.

Russia denies supporting the separatists.