A suicide bomber on a motorbike struck a joint Afghan-NATO patrol in the town of Khost on Wednesday, killing 11 Afghans, officials said.
Seventeen others were injured in the blast in the eastern town close to the border with Pakistan, where Taliban and other Islamist insurgents fighting
US-led troops have strongholds.
Amir Padsha, the director of Khost city hospital said the dead included three police officers and eight civilians.
Interior ministry spokesman Sediq Sediqqi said the bombing targeted a combined Afghan and coalition patrol passing through the town.
There was no immediate claim of responsibility but Sediqqi blamed the "enemies of Afghanistan", a phrase commonly used by Afghan officials to refer to the Taliban.
He had earlier put the initial death toll at four.
Khost is one of the most troubled regions in Afghanistan, where the Taliban have waged a bloody insurgency against President Hamid Karzai's Western-backed government since they were ousted from power in a US-led invasion in 2001.
The Haqqani network, a militant group close to Al-Qaeda and blamed for some of the most daring insurgent attacks in Afghanistan, is particularly active in the border province.