Russia sent fighter jets to Belarus on Thursday in response to a request by the country's president, after NATO beefed up its presence in light of the crisis in Ukraine.
Six SU-27 jets and three transport planes were moved to Belarus's eastern Bobruisk aerodrome, a spokesman for the Russian defence ministry told the ITAR-TASS news agency.
"The crews of the Russian jets will start joint military duties with Belarussian colleagues to carry out aerial reconnaissance and ensure the protection and defence of the air space (of Russia and Belarus)," the spokesman said.
The Belarussian defence ministry confirmed the deployment on its website, saying that the planes are set to take part in joint exercises.
Belarussian President Alexander Lukashenko on Wednesday told his security council he would ask Russia to send up to 15 jets.
"If NATO decided, together with the Americans, to ramp up their air force presence near our borders, what, should we just watch them?" Lukashenko said.
NATO has stepped up security measures in its ex-communist member countries bordering Ukraine and Russia.
The United States last week sent six additional F-15 fighter jets to bolster NATO's air patrols over the Baltic states bordering Russia.
Washington is also sending a dozen F-16 fighter jets and 300 service personnel to Poland for what it is calling a training exercise.