Two Afghan policemen also died and two others were wounded in the explosion in mountainous Shorabak district of Kandahar province, 12 miles (19 kilometers) from the Pakistan border, said Gen. Abdul Raziq, chief of the Afghan border police in the province.
"Two months ago, we cleared this area of terrorists, but still they are active there," Raziq said.
The Taliban claimed responsibility for the blast. "A bomb was planted for them in a field," Taliban spokesman Qari Yousef Ahmadi told The Associated Press in a telephone call.
Besides the seven troops killed in the bombing, the US-led coalition reported that an eighth NATO service member was killed when a helicopter crashed in the east. The US-led coalition did not release further details of the deaths.
It was the deadliest day for coalition forces in Afghanistan since April 27, when a veteran Afghan military pilot opened fire at Kabul airport and killed eight US troops and an American civilian contractor.