Four Americans were killed and three others wounded Monday by a roadside bomb near Bagram Air Base in Afghanistan, military officials said.
Three other service members were hurt, the North Atlantic Treaty Organisation alliance said.
Other reports suggested that it was a suicide bombing claimed by the Taliban, with an attacker driving an explosive-laden auto into a USA military convoy.
The base in Bagram district is located in northern Parwan province and serves as the main US air facility in the country.
"The wounded service members were evacuated and are receiving medical care", Resolute Support said in a statement. The names of the casualties are being withheld for at least 24 hours pending next-of-kin notification.
(Sgt. Justin Updegraff/U.S. Marine Corps via AP, FILE) U.S. Soldiers with Task Force Iron maneuver an M-777 howitzer, so it can be towed into position at Bost Airfield, Afghanistan, June 10, 2017.
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The US now has some 14,000 troops in Afghanistan - down from a peak of around 100,000 - majority deployed to train and advise Afghan counterparts.
He told the House Foreign Affairs Committee on March 27 that USA officials are trying to convince all parties, including Afghanistan President Ashraf Ghani and his government, to reach a reconciliation. The Taliban has balked at negotiating with the Afghans, which the group views as an American puppet organization.
"The EU encourages the government of Afghanistan and the Taliban to intensify their efforts towards a peaceful and negotiated settlement of the conflict" said the statement.
Negotiations between Khalilzad and the Taliban are expected to continue in Doha later this month.
The notion of an interim government to tide things over between the end of Ghani's term in May and an election has sparked controversy in Afghanistan, and there is as yet no clarity as to what will happen.