Russia sent two nuclear-capable bombers on a training mission over Belarus on Thursday - for the second time in two days.
It signalled a show of support from Moscow for its ally amid a migration dispute at the border with Poland.
According to Belarus' defence ministry, two Russian Tu-160 strategic bomber aircraft carried out practice bombing runs at the Ruzhansky firing range in Belarus. As part of the joint drills, Belarusian fighter aircraft simulated an intercept of the Tu-160s.
The ministry added that such training would be carried out on a regular basis.
Moscow said the bombers were in the air for more than four-and-a-half hours, intending to reflect their support for their alliance with Belarus. It added the bomber patrol "wasn’t aimed against any third countries".
Russia's strong support for its Belarusian neighbour comes amid a tense standoff this week as thousands of migrants, most of them from the Middle East, gathered on the Belarus side of the border with Poland, trying to get into western Europe.
The European Union has accused Belarus' authoritarian 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 Mr Lukashenko's disputed 2020 re-election.
Minsk has denied the allegations but says the country will no longer stop refugees and migrants from getting into the EU.
The Belarusian defence ministry accused Poland on Thursday of an "unprecedented" military build-up on the border, saying that migration control did not warrant the concentration of 15,000 troops backed by tanks, air defence assets and other weapons.
"It looks more like forming a strike group of forces," the ministry said, adding that the Polish military build-up had prompted Belarus to respond with actions "both independently and within the existing agreements with our strategic ally" – a reference to Russia.