The US military says coalition forces in Afghanistan have begun a major operation against Taleban militants in the south-east of the country.
US forces have been in Afghanistan since 2001
Operation Mountain Fury involves some 3,000 US-led troops and 4,000 Afghan security personnel, the US said.
One US soldier was killed during an attack by militants on a base in the province of Khost, the military said.
Nato-led forces in southern Afghanistan are also fighting the Taleban, but US troops are not under Nato command.
"Mountain Fury is just one of a series of co-ordinated operations placing continuous pressure on Taleban extremists across both regions of the country," Lt Col Paul Fitzpatrick of the US military said.
The operation will focus on the Taleban resistance in Paktika, Khost, Ghazni, Paktia, and Lowgar provinces, he added.
The troops are aiming to restore security as well as undertaking development and rebuilding projects, the military said.
Success would allow local governors to resume effective control of their regions, and for planned construction projects to go ahead.
A spokesman for the US military said the new operation had been in preparation for weeks but entered an operational phase on Saturday.
Separately, one US soldier died and one was injured, along with three Afghan soldiers, when Taleban fighters attacked a military base in Khost.
The resurgence of the Taleban has prompted international commanders in Afghanistan to request more troops for the ongoing mission in the country.
But Nato members were slow last week to respond to a call for extra troops by the organisation's secretary general.
Poland agreed to send 1,000 troops to the country, but they will not be deployed until next year.
The BBC's Alastair Leithead, in Kabul, says the past year has been the most violent in Afghanistan since a US-led offensive toppled the Taleban government in 2001.
Fighting in the south and east has been intense, but the insurgency also includes assassinations, school burning and the use of roadside bombs, he adds.