The United States on Tuesday sent extra jet fighters to patrol the skies over Baltic states to reinforce its NATO allies as Russia gears up for major major military drills, Lithuania's defence ministry said.

Seven US F-15 fighter jets landed at the country's northern Siauliai military air base, where NATO member Poland ran patrols using four jets over the last four-month rotation.

The beefed up contingent arrived two weeks ahead of massive military exercise "Zapad 2017" ("West") in neighbouring Russia and Belarus.

Lithuanian intelligence has warned that the "exercise scenario will simulate an armed conflict with NATO" but Moscow on Tuesday insisted they would be "purely defensive" and not directed against any specific enemy.

According to Russian deputy defence minister Alexander Fomin, the drills will involve 12,700 troops, but critics, Lithuania included, claim there could be as many as 100,000.

Belarus' military chief of staff Oleg Belokonev indicated Tuesday the exercises' scenario involves an assumed threat from neighbours to the west and said that the number of troops participating will be "13,800 servicemen."

NATO has been guarding Baltic skies since 2004, when Lithuania and fellow Baltic states Latvia and Estonia joined the defence alliance but lacked the air power to monitor their own airspace.

Last week, NATO jets were scrambled four times to intercept Russian planes approaching Baltic countries' airspace, including an Il-22 bomber and seven Su-27 fighter jets, according to Lithuania's defence ministry.

NATO has also deployed about 1,000 soldiers in each of the Baltic states and Poland in response to growing concern over Russian intentions after Moscow's 2014 annexation of Crimea from Ukraine.

souce: AFP