US authorities were forced to suspend the Defender-Europe 20 manoeuvres, originally planned for May, as the pandemic forced lockdowns in the US and Poland, where the scaled-back wargames are now underway.

More than 6,000 soldiers from the two countries, including 4,000 US troops, will participate in the exercises until June 19 at the northern Drawsko Pomorskie military training range.

"All personnel will undergo testing for COVID-19 upon arrival" and have had to undergo quarantine before or after arrival, US Army spokeswoman Beth Clemons said in a statement sent to AFP.

"Cloth face coverings, additional sanitation and other protective measures are strictly enforced" in areas where soldiers cannot abide by social distancing, she added.

"The number of participants was also reduced to allow for increased physical distance," Clemons explained.

Originally planned to be the largest joint US-Europe war games in 25 years, the drills were to have drawn about 37,000 soldiers from 18 NATO countries.

Plans had called for the US-run manoeuvres to be held in Germany, Poland and the Baltic States.

The Pentagon had wanted to send more than 20,000 soldiers to the exercises but the pandemic prompted it to freeze military movement around the world.

The new exercise will feature a Polish airborne operation and a US-Polish division-size river crossing.

Poland has long regarded the United States as the primary guarantor of its security within the NATO Western defence alliance.

US President Donald Trump upped his country's troop rotations in Poland to 5,500 personnel as part of a wider NATO response to concerns in the region triggered by Russia's 2014 annexation of territory from neighbouring Ukraine.