BRUSSELS -- The head of NATO says Russia has been sending large amounts of weapons to rebels in eastern Ukraine and stepped up its military activity around Europe and the world.
NATO Secretary-General Jens Stoltenberg told a monthly news conference in Brussels that "efforts for a lasting peace continue" despite daily violations of a September cease-fire in the conflict between Ukrainian government forces and pro-Russian separatists.
"We see a significant military buildup in and around Ukraine, large transfers of Russian advanced weapons, equipment, and military personnel to violent separatists, and a major increase in Russian military activity around Europe and beyond," Stoltenberg said.
He said Russia and the separatists are not respecting the cease-fire deal signed in Minsk, which aimed to end a conflict that has killed more than 4,300 people since April and driven East-West ties to post-Cold War lows.
The Ukrainian military accused Russian special forces of taking part in rebel attacks on the Donetsk airport, a strategically important facility that has been a focus of fierce fighting despite the cease-fire.
"These are Russian special forces. It's already the third day that they've been trying to do something," the Reuters news agency quoted military spokesman Andriy Lysenko as saying by telephone.
Lysenko said three Ukrainian servicemen had been killed in the previous 24 hours in intensified artillery strikes from the rebels that he linked to the arrival of another large aid convoy from Russia on November 30.
"The new humanitarian convoy arrived and the terrorists received ammunition for heavy artillery ... therefore they are able to increase the intensity [of attacks]," he said.
Russia has dispatched several shipments of aid to alleviate what it says is a drastic humanitarian situation in eastern Ukraine, but the pro-Western government in Kyiv accuses Moscow of using the shipments to send military equipment to separatists.
Stoltenberg said, "The best way of improving the humanitarian situation in eastern Ukraine is to stop the violation of the Minsk agreement, to respect the cease-fire, and we have seen that the separatists and Russia [are] not doing that."
Russia denies involvement in the conflict despite what Kyiv and NATO say is evidence of direct Russian military support for the rebels, who hold large portions of eastern Ukraine's Donetsk and Luhansk regions.
Painting a broader picture of Russia's military activity, Stoltenberg said NATO aircraft have been scrambled more than 400 times this year to intercept Russian aircraft, an increase of 50 percent over such incidents last year.
He said that "in the Baltic region, the increase has been even stronger."
Stoltenberg said NATO has "already boosted our presence in the eastern part of our alliance."
"We have five times more planes in the air. Our forces start and exercise every two days and we have also increased the number of ships in the Baltic and the Black seas."
A senior Russian official asserted that it is NATO which is stirring up tension in the Baltics.
Deputy Foreign Minister Aleksei Meshkov told the Interfax news agency on December 1 that Moscow believes NATO is destabilizing northern Europe by holding military exercises there and "transferring aircraft capable of carrying nuclear arms" to the Baltic states.
Meshkov warned that Moscow will do all it can "to firmly safeguard the security of Russia and its citizens ... no matter which part of our country it concerns."
At the same time, he said Russia-NATO relations have not reached the "point of no return" despite serious disagreements.
Meshkov's statement came after NATO's top military commander voiced concern that Russia might be moving nuclear capabilities to the Crimean peninsula, which Russia annexed from Ukraine in March in what Kyiv and the West said was an illegal land grab.
U.S. Air Force General Philip Breedlove said in Kyiv on November 26 that the United States was "very concerned with the militarization of Crimea."
The rebels have strengthened their grip over territory they control by holding November 2 elections denounced by Kyiv and the West as illegitimate.
Russia has not recognized the separatists' claims of independence from Ukraine, but Kremlin critics fear Moscow will use them to keep the France-sized nation destabilized for years to come and hinder its efforts to integrate more closely with the European Union and NATO.
The EU enlargement commissioner, however, suggested on December 1 that the crisis has strengthened Ukranians' sense of identity.
"The last year has certainly contributed to Ukraine -- and also Ukrainians -- having more then ever defined themselves as a nation," EU Neighborhood Policy and Enlargement Negotiations Commissioner Johannes Hahn said at a briefing in Brussels.
With reporting by Reuters and AP