Clashes between Pakistani troops and pro-Taliban militants have left at least six civilians dead in the country's violent tribal region bordering Afghanistan.

During the fighting late Monday mortar shells ripped through civilian homes, killing six people in Landi Kotal Khyber, AFP on Tuesday quoted local officials as saying.

The incident took place after a group of 50 heavily-armed gunmen stormed a Frontier Corps (FC) checkpoint in Landi Kotal.

They had to retreat after facing the government forces' return fire which killed six of the militants.

It was not clear who launched the mortars.

Officials said FC troops backed by helicopter gunships joined the offensive against pro-Taliban forces in the neighboring Orakzai district and nearby Hangu, killing at least 12 militants.

The militants in the region were believed to be responsible for recent attacks in the northwestern city of Peshawar.

On Tuesday, Pakistan's military officials said they killed at least 18 rebels and arrested another six in their new offensive in South Waziristan.

Islamabad says it launched a major offensive on October 17 in a bid to wipe out an estimated 10,000 militants holed up in South Waziristan.

MRS/MTM/DT