* Russian fighters, bombers involved in drills
* Tension high between NATO and Russia over Ukraine (Adds details, context)
By Steve Gutterman
MOSCOW, March 19 (Reuters) - Russia's military started large-scale aviation exercises in the northwest on Wednesday, officials said, close to Baltic ex-Soviet republics that are members of NATO and wary of Russia after its annexation of Crimea.
The exercises involving jet fighters and bombers were being conducted in regions that do not border Ukraine. A senior Russian military source said they had been planned in December and had no political significance.
Interfax reported that the drills would involve more than 40 Sukhoi and MiG warplanes and were being held in regions including Leningrad, which borders NATO-member Estonia and Finland, and Karelia, which shares a long border with Finland.
The drill ends in late March, it cited a spokesman for the Western Military District, Colonel Oleg Kochetkov, as saying.
Russia has held major military exercises in regions near Ukraine twice in recent weeks, raising concern in Kiev and the West that Moscow could have designs on eastern Ukrainian regions where there are many Russian speakers.
President Vladimir Putin sought to assuage those fears on Tuesday, saying Russia did not want to take over other regions or partition Ukraine. But he has reserved the right to send in the military to protect Russians there if needed.
Russia sent thousands of soldiers to Crimea in the buildup to a weekend referendum in which the Russian-majority region voted overwhelmingly to leave Ukraine and join Moscow. Ukraine and Western governments have dismissed the referendum as a sham.
The United States has emphasised NATO's collective commitment to protect member states, sending F-16 fighter jets to Poland for drills last week and holding joint exercises with other allies that were once Soviet satellites.
In Warsaw on Tuesday, U.S. Vice President Joe Biden accused Russia of a "land grab" in Crimea and said the United States may conduct more drills with NATO allies in the region.
(Additional reporting by Alexei Anishchuk; Editing by Janet Lawrence)