Seven US soldiers have been killed in two bomb attacks in southern Afghanistan, the Nato-led International Security Assistance Force (Isaf) says.
Five troops were killed by a roadside bomb in one incident while two others died in a separate bomb attack, Isaf said in a statement.
Witnesses in Kandahar said a US Army vehicle hit a bomb in the early afternoon, the Associated Press said.
Fourteen US soldiers have been killed in Afghanistan in the last three days.
Meanwhile, the governor of the Lalpor District in Nangarhar Province was killed by a car bomb in the city of Jalalabad on Monday, according to police spokesman Ghafor Khan.
The bomb, which had been planted on the vehicle, exploded while it was driving into a government compound, said Mr Khan.
Governor Syad Mohammad Palawan was reportedly travelling to a meeting of provincial security and political leaders when he was killed.
Increased troop numbers
The US has sent an extra 30,000 troops to Afghanistan since December 2009 in an effort to defeat the Taliban.
US troops now comprise roughly 100,000 of the 120,000 foreign military soldiers in Afghanistan, most in the south and east where the Taliban is most deeply entrenched.
Foreign troops fighting the Taliban operate under US and Nato command and are supporting Kabul's Western-backed government against a Taliban-led insurgency that has gained strength in recent years.
News of the most recent attacks comes a week after a senior US general in Afghanistan said President Barack Obama's July 2011 deadline to begin pulling troops out of the country was encouraging the Taliban.
The White House is expected to review the Afghan war in December.
More than 1,200 US soldiers have died in Afghanistan since the conflict began in 2001.