NATO's top commander said Wednesday that Russia was "increasing" the number of troops and weaponry along the border with Ukraine.

"The number of troops along the (Ukrainian) border is increasing. It is well over 12,000," General Philip Breedlove told reporters at the end of his one day visit to Kosovo, where he inspected the alliance's peacekeeping mission.

"The number of battalion task groups, specials, Spetznaz (special forces) units, air defence units, artillery units are all increasing," he said.

According to Breedlove, the supreme allied commander of NATO, the Russian weaponry contingents deployed to the crisis area includes "every kind of weapon, supplies, man portable weapons, field weapons, armoured vehicles, all of the weapons."

"We watch the materials move from inside the central military district of Russia to the area of Rostov, where they are assembled, met, trained, moved towards the border, and then we see them across the border being employed in the Ukraine," Breedlove said.

In mid-July NATO sounded the alarm over a Russian build-up on the border to up to 12,000 after a drop-off to fewer than 1,000 in June.

The European Union and the United States have imposed harsh new sanctions against Russia, targeting the finance, defence and energy sectors to increase the cost to Russia of its intervention in Ukraine.