BELGRADE, Serbia — Serbia says it will purchase Russian combat jets that are likely to add to tensions in the Balkans amid Moscow’s apparent efforts to prevent the volatile European region from joining Western institutions.

Serbian Prime Minister Aleksandar Vucic said Monday he will travel to Moscow later this week to sign a deal that will include six MiG-29 fighters that he says are needed “to protect our freedom and sovereignty.”

Although formally seeking EU membership, Serbia has been sliding toward its traditional Slavic ally Russia. Moscow has launched a major propaganda effort to keep it away from the West.

The regional tensions have risen in the wake of an alleged coup attempt in October by Serbian and Russian nationalists against Montenegro’s pro-Western government for its efforts to join NATO.