Two days after the explosion of a suspected nuclear-powered cruise missile undergoing testing Aug. 8, two monitoring stations nearest the site of the accident stopped transmitting data, Lassina Zerbo, who heads the Comprehensive Nuclear Test Ban Treaty Organization, told The Wall Street Journal.

The Russian monitoring stations, called Dubna and Kirov after the places where they are located, were contacted immediately about the data disruption, Mr. Zerbo wrote in an email Sunday to the Journal, and Russian officials responded that they were experiencing “communication & network issues.”

“We are pending further reports on when the stations or the communication system will be restored to full functionality,” Mr. Zerbo added. He declined to speculate on what caused the outage.