Afghan officials say at least 90 people were killed and 400 wounded in Wednesday's attack.
This was the worst terror attack in Kabul after March 2017 when 30 people were killed after terrorists dressed as doctors stormed Sardar Daud Khan Military Hospital. The attack was committed with a tanker during morning rush hour, in an area that houses many embassies and ministries, AD reports.
One Afghan security guard was killed and others were likely among the dead, Gabriel said.
The US has about 8,400 troops in Afghanistan, with another 5,000 from North Atlantic Treaty Organisation allies.
In the past year, USA troops have largely focused on thwarting a surge in Taliban attacks. The U.S. Embassy and the North Atlantic Treaty Organisation mission in Kabul, located about a kilometer away from the site of the explosion, both condemned the attack.
The neighborhood is considered Kabul's safest area, with foreign embassies protected by dozens of 10-foot-high blast walls and government offices, guarded by police and national security forces.
The US embassy and the North Atlantic Treaty Organisation mission are about half a mile from the site.More news: 'Kushner more than willing to answer Russia-related questions'
The Taliban, which has recently begun its annual spring offensive - and is the strongest terrorist organization in the country - has denied responsibility for the attack.
"I've never seen such a powerful explosion in my life", said Mohammad Haroon, who owns a nearby sporting goods store.
She expressed condolences and honest sympathy for the victims and their families. She adds that for now, Germany will suspend deportations of rejected Afghan asylum seekers, to ease the workload of the embassy staff in Kabul. The Taliban - now in the midst of their annual "spring offensive" - tweeted that they were not involved and "strongly condemn" the blast.
The Afghan interior ministry says 64 people were killed and as many as 320 were wounded in the massive vehicle bombing in Kabul earlier in the day. Germany's foreign ministry indicated in a tweet that its embassy was damaged in the blast and that several German citizens were injured.
Operation Resolute Support, the NATO-led worldwide mission to support Afghan forces, is focused this year on building Afghan forces' offensive capability on the battlefield, Salvin added.
U.S. troops have been in Afghanistan for almost 16 years, where the government and coalition allies are battling several terror groups, including the Taliban and ISIS.
Associated Press writer Rahim Faiez reported this story in Kabul and AP writer Kathy Gannon reported from Islamabad.