An explosion rocked the Afghan southern city of Kandahar Thursday morning, leaving seven people dead and 17 others injured, said the coalition forces in a press release.
It said the explosion occurred near the intersection of Highway 1 and 4 at 8 am (0330 GMT).
The explosion was caused by a bomb on the bus and is believed to be a deliberate attack against Afghan civilians, it added.
Tom Koenigs, the special representative of the UN secretary general for Afghanistan, expressed "shocked and saddened" by this morning's bus explosion in Kandahar city.
"There could be no justification for such a bloody attack against innocent civilians," he denounced.
According to deputy Kandahar provincial police chief Abdul Hakim Hungar, the targeted bus was carrying Afghan laborers working for the U.S.-led military at the Kandahar airport.
It is the first time the anti-government militants directly target civilians serving U.S. military interest in the post- Taliban nation, a tactic common in Iraq to keep locals away from contacting U.S. forces.
The bloody explosion took place just one day after the coalition troops' announcement to launch a massive operation dubbed as "Mountain Thrust" to root out Taliban-linked militants in the south.
In recent two days, There were other attacks or conflicts in this country. on Wednesday, the firefight between Afghan police and Taliban militants claimed the life of one anti-government militia in the southern province. In Zabul province, three Afghan police were killed as their joint patrol team came under Taliban attack on Wednesday night.
And also, two local employees of a Turkish construction company were killed and another wounded as a planted mine struck their vehicle in the southwest of Nimroze province Thursday.
Kandahar, the former stronghold of Taliban and neighboring provinces of Zabul, Uruzgan and Helmand have been the scene of unexpected increasing insurgency over the past one month during which some 500 people have been killed.
Taliban-led insurgence has claimed the lives of more than 800 people including some 30 American soldiers since beginning 2006.