MOSCOW (AP) — A pair of nuclear-capable Russian long-range bombers patrolled the skies over Belarus on Saturday on a mission intended to underline close defense ties between the two allies amid tensions with the West.

The Russian Defense Ministry said two Tu-22M3 flew a four-hour mission to practice “performing joint tasks with the Belarusian air force and air defense.” The bombers were escorted by Belarus' Su-30 fighter jets, which Russia has supplied to its ally.

Saturday’s Russian bomber patrol marked a third such mission since last month.

The patrol flight comes amid Western concerns over a Russian troop buildup near Ukraine that raised fears of an invasion. Moscow has denied plans for such an attack, but urged the West to provide security guarantees that would exclude NATO's expansion to Ukraine and the deployment of the alliance's weapons there — demands that are almost certain to be rejected by the U.S. and its allies.

Some Ukrainian officials have voiced concern that Russia may use the territory of its ally Belarus for attacking Ukraine.

Moscow has strongly supported Belarus amid a tense standoff last month when thousands of migrants and refugees, most of them from the Middle East, gathered on the Belarusian side of the border with Poland in the hope of crossing into Western Europe.

The European Union has accused authoritarian Belarusian President Alexander Lukashenko of encouraging illegal border crossings as a “hybrid attack” to retaliate against EU sanctions on his government for its crackdown on internal dissent after Lukashenko’s disputed 2020 reelection.

Amid tensions with the West, Lukashenko said last month that his country would be ready to host Russian nuclear weapons.

The Belarusian leader wouldn’t elaborate on what kind of weapons Belarus would be willing to accommodate, but noted that the ex-Soviet nation has carefully preserved the necessary military infrastructure dating back to the time of the USSR.

Russian Foreign Minister Sergey Lavrov has described Lukashenko’s offer as a “serious warning prompted by reckless Western policy.”