And an eighth NATO serviceman died in a helicopter crash making it the deadliest day for coalition forces in the country since Osama bin Laden was killed on May 2.
The deaths came shortly after neighbouring Pakistan told the U.S. government to cut the number of military trainers there by a half.
Soldiers routinely patrol fields in Afghanistan on the lookout for terrorists. But their mission went tragically wrong on Thursday when a bomb exploded killing seven.
The Taliban claimed responsibility for the blast, which also killed two Afghan policemen near the Pakistan border in an area that was thought to be free of terror.
The soldiers were on foot patrol in a field in the Shobarak district of Kandahar province when the bomb went off.
Pakistan has told the United States to halve the number of its military trainers in the country, the latest sign of spiralling distrust between the two allies since the killing of Osama bin Laden.
The killing of bin Laden by U.S. special forces sparked a wave of militant attacks and 13 people were killed in the latest suspected suicide bombing in a north-western town on Thursday.
Pakistan informed the United States in the last week or two that it would not need some U.S. special forces trainers advising the Pakistani military, the Pentagon said.
"We don't need unnecessary people here. They cause problems for us instead of being helpful," said a Pakistani security official who said the withdrawal might start by early June.
Another Pakistani security official said the decision was made because of concerns over the Americans' security and because "resentment all around was very high."
General Tefeer Khan Ghogyaria, who oversees Afghan border police in three southern provinces described the explosion as 'a big, powerful blast.'
"A container of explosives was placed in the ground and it exploded when the NATO forces were passing,' he said.
Tens of thousands of U.S., NATO and Afghan forces have been working for months to rout the Taliban from their strongholds in the south.
'Two months ago we cleared this area of terrorists, but still they are active there,' said Afghan border police chief Gen. Abdul Raziq.
Fundamentalist groups promised retaliation for the death of bin Laden, who was killed when U.S, Navy Seals stormed his compound in Abbottabad, Pakistan.
Details of the eighth death, including the nationality of the victim, were not released.
The body count was the highest for NATO troops since April 27, when a veteran Afghan military pilot opened fire at Kabul airport and killed eight U.S. troops and an American civilian contractor.
When bin Laden died, insurgents announced the start of a spring offensive against NATO forces and Afghan authorities, which have been bracing themselves for a series of spectacular and complex attacks.
The effectiveness of the Taliban's long-awaited spring campaign, code-named Badr after one of the Prophet Muhammad's decisive military victories, could affect the size of President Barack Obama's planned drawdown of U.S. troops in July.
Coalition forces have been bracing themselves for reprisals since Osama bin Laden was killed by U.S. special forces in a surgical strike on his compound in Abbottabad, Pakistan
General David Petraeus, the top U.S. and NATO commander in Afghanistan, has said the size of the withdrawal will depend on conditions on the ground.
The alliance has committed itself to handing over control of security in the country to Afghans by 2014.
Thirty-eight international service personnel have been killed so far this month, including at least 13 Americans. So far this year, 189 coalition troops have died in Afghanistan.
