Image: AP

According to reports, a fourth bomb planted in the attack this morning on Brussels failed to detonate.

At least ten people died at the city’s international airport when a pair of bombs exploded around 8 a.m. Tuesday. Another twenty were killed when a bomb exploded inside a subway car pulling out of the Maelbeek metro station. Between the two locations, more than 230 people were injured.

The carnage could have been worse, the New York Times reports—a third bomb planted at the airport apparently failed to detonate. Authorities were able to neutralize it on the scene with “a controlled action.”

Officials tell the AP the bombs appear “sophisticated.” ISIS has since claimed responsibility for the attack.