Islamabad, Pakistan (CNN) -- Two militants and a passerby were killed in a rare clash between security forces and Taliban fighters in Pakistan's tribal belt, officials and a witness told CNN Wednesday.
The skirmish took place in Miranshah, North Waziristan, a district in Pakistan's tribal region where Pakistani security forces seldom fight the Taliban.
A Pakistani intelligence official and a local political official said the fighting started when armed militants ambushed a military convoy that was on its way to destroy a hospital that was suspected of being used as a Taliban hideout.
Pakistani troops backed by at least three helicopter gun ships fought back the militants in a firefight that lasted at least two hours, a resident of Miranshah told CNN by phone.
The clash comes a day after a planted bomb just outside Miranshah killed two security forces and injured 15 others.
U.S. officials call North Waziristan a safe haven for al Qaeda-linked militants who attack American soldiers across the border in Afghanistan.
Despite increasing pressure by Washington to launch an offensive in North Waziristan, the Pakistani Army has refused, saying its troops are stretched too thin with other operations in northwest Pakistan.
The army's reluctance to attack the Taliban in the district has fueled suspicions that the Pakistani military has links to militant groups in North Waziristan that are undermining the NATO operation in Afghanistan.
Pakistani military officials have repeatedly denied the allegations.
Elsewhere in northwest Pakistan, more than 100 armed militants from Afghanistan crossed the border into the district of Upper Dir and killed a leader of a pro-government, anti-Taliban volunteer militia, a Pakistani military official told CNN.
The militants also set fire to 11 shops and three schools in the village of Nusrat Dara.
In recent years militants have increasingly targeted volunteer militias that are established by local villagers to keep out the Taliban from their towns and villages.
The military official asked not to be named because he was not authorized to speak to the media.
