The US Central Command confirmed that two US troops were killed, but provided no details.
It said additional information was being withheld until 24 hours after notification of next of kin was complete.
Attacks on US and Afghan forces have intensified in the run-up to presidential elections and violence marred the start of the campaign on the weekend, after President Ashraf Ghani insisted “peace is coming” to the war-torn nation.
At least 20 people were killed and 50 others wounded on Sunday in an attack targeting the Kabul office of Ghani’s running mate, Amrullah Saleh.
The violence came on the first day of campaigning for the elections, serving as a grim reminder of Afghanistan’s woeful security situation and the sort of mayhem and murder that have beset previous polls.
The attack began around 4:40pm, when a huge blast struck near the office of Green Trend, a youth and reform-focused civil society organisation Saleh heads. He escaped without serious injury, his office said.
The interior ministry said the assault began when a suicide bomber detonated an explosives-packed car at the entrance to the building, then three attackers ran inside.
After about six hours the siege ended with all attackers killed and the rescue of about 150 people who had been trapped in the building, according to the interior ministry, which also provided the toll of 20 dead and 50 wounded.
Earlier on Sunday, a buoyant Ghani kicked off his campaign by insisting “peace is coming,” after nearly 18 years of conflict, and that pivotal talks with the Islamist extremist Taliban would take place.
He is hoping to fend off challenges from 17 other candidates to score a second term at twice-postponed presidential elections now slated for September 28.
On Saturday Ghani’s peace minister, Abdul Salam Rahimi, said direct talks would take place with the Taliban within two weeks as part of a larger, US-led push for peace.
Such a development could be crucial, as the Taliban — who now control or influence about half of Afghanistan — have so far refused to speak to Ghani’s government. They consider the Kabul administration illegitimate.
War aside, the country faces a host of major issues ahead of the election, including rocketing crime, a lacklustre economy, soaring unemployment, and crumbling infrastructure.
Voters are despondent about the prospects of a fair election. Many worry about a repeat of violent attacks on previous polling stations by the Taliban and other insurgent groups trying to undermine Afghanistan’s fragile democracy. Ghani insisted this year’s vote would be “clean”, but distrust is rife.
Sayed Jan, a 27-year-old student, said he won’t be voting as he has lost faith since the 2014 election that was mired in allegations of fraud and ballot stuffing.
“We have been betrayed by the candidates in the past. We cannot trust them this time,” he said.
“We need peace in Afghanistan instead of elections. Even if I vote, the election will be fraudulent.”