"The presidents of Belarus and Russia decided to continue inspections of the readiness of Union State forces," the Belarusian defence minister Victor Khrenin said in a statement.

He said the decision was taken due to increased military activity along the Belarusian and Russian borders and because of an "escalation" in east Ukraine.

The drills in Belarus -- which had been due to conclude Sunday -- have exacerbated tension between Moscow and Western capitals over a feared Russian attack on Ukraine.

Washington had previously said that the Kremlin had dispatched an estimated 30,000 troops to the exercises across ex-Soviet Belarus, including on Ukraine's northern border.

The Belarus defence ministry said upcoming stages of the large-scale drills would continue the aim of ensuring a sufficient military response to any external threats.

It did not specify an end date.

Belarus strongman Alexander Lukashenko has become an increasingly close ally of Russian leader Vladimir Putin.

This bond grew stronger after Moscow threw its political weight behind Minsk during large anti-government protests in 2020.

Belarus's embattled opposition had feared that Russian troops might not leave their country following the drills, a move that would cement closer ties between Putin and Lukashenko.

Belarus Foreign Minister Vladimir Makei however said shortly after the drills began earlier this month that "not a single" Russian soldier would remain in the country after the massive joint manoeuvres end.

The French presidency had also said that Emmanuel Macron had received assurances from Putin that Russian troops would depart following the drills.