The US army's commander in Europe has accused Russia of using its military campaign in Syria as a "live-fire training opportunity".
Lieutenant General Ben Hodges said Russia's "disregard for civilian casualties ... is not the conduct of a nation that wants to be treated like a superpower".
Russia's defence minister said on Thursday that its air force had killed 35,000 fighters in Syria.
But Russia has been accused of using heavy weapons in civilian areas.
It has consistently denied targeting civilians.
Russia's aerial intervention in the Syrian conflict last year has helped the Syrian army capture eastern Aleppo. But it has further heightened tensions with the West, after it annexed the Crimean peninsula from Ukraine in March 2014.
Defence Minister Sergei Shoigu said 162 types of modern armaments had been tested during the campaign in Syria, which included 18,800 aerial sorties.
"What we see in Syria of course is a demonstration of capabilities and using weapons that are not necessary," General Hodges said.
President-elect Donald Trump is known to want better relations with Moscow, but Gen Hodges said the US military was pushing ahead with plans to bolster its presence in Europe.
"All the indications show we are going to continue our commitment," he said.
President Vladimir Putin gave a bullish account on Thursday of Russia's military strength at the defence ministry's final meeting of 2016, describing it as "currently stronger than any potential aggressor".
But he said Russia had to "strengthen the military potential of strategic nuclear forces, especially with missile complexes that can reliably penetrate any existing and prospective missile defence systems".
Mr Shoigu accused Nato of doubling the intensity of its military exercises, mainly with the focus on Russia.
He singled out the UK, accusing British armed forces of using Russian tanks and army uniforms to identify the enemy during exercises on Salisbury Plain in southern England.
"The last time this way of training troops was used was by Nazi Germany," he added.
Syrian army claims control of Aleppo
The Syrian army says it has retaken complete control of Aleppo, giving President Bashar al-Assad his biggest victory in a civil war that has lasted nearly six years.
The army said the last group of rebels and their families have been evacuated from a small eastern enclave, and rebel resistance in the city is at an end.
At least 34,000 people, both civilians and fighters, have been evacuated from east Aleppo in wintry conditions over the past week.
United Nations' special envoy to Syria Staffan de Mistura said many have gone to the city of Idlib.
Mr Assad has declared that the war is far from over and his armed forces will march on other rebel-held areas.
- BBC / Reuters