Press TV reports.
The incident occurred on Monday night when Taliban militants targeted the US base in Kandahar's Shah Wali Kot District, provincial Afghan officials confirmed.
The sources said seven militants were involved in the terrorist operations, noting that all the seven were killed by Afghan security forces.
The Taliban, however, claimed 40 US soldiers were killed in the "massive" strike. They said 17 Taliban members were also wounded in the attack.
The militant group has a reputation for exaggerating the enemy's losses, yet the attack is said to be one of the heaviest ever against the US-led foreign militaries in Afghanistan.
According to official figures, more than 3050 US-led soldiers have been killed in Afghanistan since the invasion of the country over a decade ago.
The increasing number of military casualties in Afghanistan has caused widespread anger in the US and other NATO member states, undermining public support for the Afghan war.
The US-led war in Afghanistan began in 2001. The offensive removed the Taliban from power, but insecurity continues to rise across Afghanistan, despite the presence of about 130,000 US-led troops.
Ten US soldiers have been wounded after a US military base came under attack in Afghanistan's southern province of Kandahar,