A massive car bomb targeting a U.S.-led NATO mission convoy killed at least 12 people, including three Virginia-based American civilian contractors, near a hospital during rush hour Saturday, the latest in a series of deadly attacks that have struck the capital in recent weeks.

The assault unfolded at 4:20 p.m. outside Shinozada Hospital in a middle-class enclave of the capital, a few miles from the heavily fortified American Embassy. The blast was so powerful that it could be heard in faraway neighborhoods and prompted the embassy to blare its emergency sirens. Nearby vehicles, including a school minivan, were severely mangled, some in flames.

In addition to those killed, as many as 66 people were wounded in the attack, said Wahidullah Mayar, a Health Ministry spokesman. In a statement, U.S. Army Col. Brian Tribus, a military spokesman for the NATO Resolute Support Mission, said that one of the civilian contractors was killed in the attack and the other two later died of their wounds. Their identities were not released because their families had not been notified.

The Americans worked for DynCorp International, a private military contractor based in McLean, Va. In a statement, the company said it extended “its thoughts and prayers to all involved and to their families and loved ones.” It declined to comment further.

“Instead of seizing an opportunity to embrace peace, insurgents have again chosen violence in an attempt to remain relevant,” Brig. Gen. Wilson Shoffner, the U.S.-led coalition’s deputy chief of staff for communications, said in a statement. “Regardless of the target of their attacks, insurgents continue to inflict a heavy toll on innocent Afghan civilians.”

Afghan security forces and British soldiers inspect the site of a suicide attack in the heart of Kabul, Afghanistan, Saturday. (Massoud Hossaini/AP)

Saturday’s bombing was the latest in a wave of deadly attacks in the capital that have killed more than 50 people since the announcement by Afghan authorities of the death of the Taliban’s spiritual leader, Mohammad Omar. Since U.S. and NATO forces officially ended their combat mission in December, the Taliban and other militant groups have intensified their attacks in many areas of the country.

On Saturday evening, Taliban spokesman Zabiullah Mujahid claimed in a statement that the group was not behind the bombing. But Mujahid had also previously denied Omar’s death. It’s possible, though, that other militant groups such as the Pakistani-based Haqqani network could have carried out the attack.

The U.S. Embassy condemned Saturday’s bombing in a statement, saying that “our thoughts and prayers are with the victims and their families who suffered as a result of this attack.”

Mohammad Sharif contributed to this report.

Read more:

A divided Taliban clings to war in wake of leader’s death

Pakistan fears that U.S. will slash military aid over counterterror efforts

Taliban leader Mohammad Omar is said to have died in 2013