But the most significant causes for concern came late Friday, when explosions hit the Nur Khan air base in Rawalpindi, Pakistan, the garrison city adjacent to Islamabad.
The base is a key installation, one of the central transport hubs for Pakistan’s military and the home to the air refueling capability that would keep Pakistani fighters aloft. But it is also just a short distance from the headquarters of Pakistan’s Strategic Plans Division, which oversees and protects the country’s nuclear arsenal, now believed to include about 170 or more warheads. The warheads themselves are presumed to be spread around the country.