In two Facebook posts, Mutombo confirmed he is safe and unharmed.
According to CNN's Greg Botelho and Catherine E. Shoichet, ISIS is claiming responsibility for the coordinated attacks, which occurred at Brussels Airport and the Maelbeek metro station. At least 30 people have died, and another 230 were wounded.
In retirement, Mutombo has focused on humanitarian work. The NBA named him the league's global ambassador in 2009, and he continues to work with the Dikembe Mutombo Foundation, which he started in 1997 with the goal of improving life in his native Democratic Republic of the Congo.
The eight-time All-Star had recently traveled to DR Congo's capital, Kinshasa, as part of his work with his charity, per the Dikembe Mutombo Foundation's Facebook page.