WASHINGTON (Reuters) – Some Washington D.C. National Guard troops have tested positive for the coronavirus after being deployed to the city to respond to protests over the death of an African-American man in police custody, the military said on Tuesday.

About 1,300 D.C. National Guard troops were sent to the capital to back law enforcement during demonstrations that erupted over the death of George Floyd, a 46-year-old black man who died in Minneapolis police custody after being pinned beneath a white officer’s knee for nearly nine minutes.

The National Guard said in a statement it would not reveal how many personnel had tested positive because of “operational security.”

It added the troops were screened for coronavirus before being deployed and are screened before leaving their posts.

“At a minimum, this screening will consist of an assessment of exposure history, a temperature check, a check for COVID-19 signs and symptoms, and review any past COVID-19 testing,” the statement added. The news was first reported by McClatchy.

There has been concern that large protests around the United States and globally may increase the spread of coronavirus.

Last week, Australian authorities moved to scupper protests over Floyd’s death, saying large gatherings risk new coronavirus infections.

British Health Minister Matt Hancock said on Sunday that anti-racism protests attended by thousands of people in London and other major British cities “undoubtedly” risk causing an increase in the number of COVID-19 cases again.