Pakistani forces used aircraft and artillery on Sunday as they stepped up an assault aimed at eliminating Pakistani Taliban commander Baituallah Mehsud, Reuters reported.

Security forces have secured much of the scenic Swat Valley, northwest of Islamabad, in the past six weeks and the military plans to extend its offensive to al Qaeda ally Mehsud, holed up in the South Waziristan region near the Afghan border.

The military action came after Taliban gains raised fears for the future of nuclear-armed Pakistan, a vital ally for the United States as it strives to defeat al Qaeda and stabilise Afghanistan.

A full-scale offensive has not yet begun in South Waziristan but fighter jets have been attacking Mehsud's positions in recent days, and did so again on Sunday.

"It's very scary. Jets have carried out heavy bombing. I saw billows of smoke and dust coming from houses that were hit," Jahangir Barki, a residents of Wana, South Waziristan's main town, told Reuters.

Security forces also fired artillery at an office of a top militant commander allied with Mehsud, Maulvi Nazir, residents said. The commander was not there at the time, they said.

The military has said it is trying to clear militants from a stretch of the main road linking Wana with North West Frontier Province.

Al Qaeda leader Osama bin Laden is believed to be hiding out in a militant enclave somewhere in the ungoverned ethnic Pashtun tribal lands along the Afghan border.