MOSCOW, March 27 (Xinhua) -- Russian and Tajik forces troops started on Monday a four-day counter-terrorist exercise in the southern part of Tajikistan, the Russian Defense Ministry said in a statement.

"The servicemen will improve cooperation between the force groupings while countering conditional illegal armed formations," said the statement, adding that both ground troops and air forces will be mobilized in the exercise.

As a traditional partner to Russia, Tajikistan is a member of the Collective Security Treaty Organization, a Russia-led military alliance established in 1992.

Russia stations its 201st military base in Tajikistan, which now houses the largest ground troops of the Russian Armed Forces outside its territory.

Tajikistan shares a 1,300-km border with Afghanistan. Russian President Vladimir Putin visited Tajikistan last month, agreeing to beef up efforts to protect the Tajik-Afghan border.