NATO and the Pentagon on Friday rejected as Moscow's denials of a major buildup of air and ground forces on Ukraine's borders.

In calling on Russia to withdraw the estimated 35,000-40,000 troops, NATO released more commercial satellite photos to rebut Moscow's claim that previous images were of a military exercise last summer in the same general area bordering Ukraine.

The release of the additional images would "clearly show that the claims of Russian officials are categorically false," NATO said in a statement.

At the Pentagon, Army Col. Steve Warren backed up the NATO statement and said "we don't think there's any question in anyone's mind that the Russians have massed troops on the border."

Earlier, Russia's official RIA-Novosti news agency quoted a senior official of the Russian General Staff as saying that the photos put out by NATO on Thursday showed "units of the Russian Southern military district, which were conducting various exercises last summer, including near the Ukrainian border."

The additional photos released Friday showed the border areas unoccupied before last month, NATO said.

"There is no evidence of any military activity in these areas in 2013 or early 2014," NATO said.

When all the images are viewed together, "it is clear that the military buildup of forces occurred in early March 2014," NATO said.

"[NATO] stands firm in its assessment that Russian forces in the vicinity of the border with Ukraine number in the range of 35,000 to 40,000 troops and are equipped with infantry fighting vehicles, tanks, combat aircraft, logistics, and artillery," the statement said.

"These forces are destabilizing to the region, which is why the North Atlantic Council has repeatedly called upon Russia to de-escalate the situation by withdrawing troops from the border with Ukraine," the statement said.

The tensions over Russia's takeover of Crimea and unrest in the Russian-speaking eastern regions of Ukraine were expected to come to a head next week in talks involving the U.S., Russia, Ukraine and the European Union aimed at defusing the crisis.

Air Force Gen. Philip Breedlove, the NATO commander, was expected to present a plan next week for bolstering the defenses of alliance members bordering Russia.

One aspect of Breedlove's plan was consideration of expanded naval patrols and exercises in the Black Sea.

In an interview Thursday with Agence France Presse, Romanian Foreign Minister Titus Corlatean was clear in what he thought should come from Breedlove's plan.

"Romania has concrete expectations of a redeployment and an eastward repositioning of NATO's naval, air and ground forces," Corlatean said. "The Black Sea region must be a top priority for NATO and the E.U.," he said.

The Aegis missile destroyer Truxtun was in the Black Sea last month at the height of the Crimea crisis, and the Aegis missile destroyer Donald Cook entered the Black Sea on Friday over protests from Moscow.

The Truxtun's Black Sea visit for exercises with the Romanian and Bulgarian navies had been planned earlier but the passage of the Cook into the Black Sea was more open-ended. Pentagon spokesman Warren said "we have not finalized which port visits the Cook will make."

-- Richard Sisk can be reached at richard.sisk@monster.com