An artillery barrage supported by attack helicopters began at first light on Tuesday to the east of the town of Wana, in Pakistan's lawless South Waziristan tribal area, where security forces have been battling rebels since March.
"There have been reports that militants, including foreigners, have scattered, and this operation is to look for them," said a security official.
The offensive was launched as US Deputy Secretary of State Richard Armitage was in Islamabad for talks with President Pervez Musharraf and other officials on a range of issues, including the US-led "war on terror".
Pakistan says several hundred foreign fighters, including Uzbeks, Chechens and Arabs, supported by Pakistani tribal allies, are operating in South Waziristan, and has vowed to remove them.
Residents in the area, 400km southwest of the capital, Islamabad, said they could hear artillery and helicopters in action.
"So far six miscreants have been killed and the security forces have lost two soldiers and a few more have been injured," said military spokesman Major-General Shaukat Sultan. "The operation is going on."
One resident said government forces appeared to be concentrating their attack along a road in the Spinkai Raghzai region, a stronghold of Abd Allah Masud, a Pakistani fighter whose men kidnapped two Chinese engineers last month.
Abd Allah Masud is wanted by
One of the Chinese men was killed in a rescue attempt, the other was freed. Masud is a former inmate of the US military prison in Guantanamo Bay, Cuba.
Hundreds of people - rebels, Pakistani troops and civilians - have been killed since the government began its campaign to clear South Waziristan in March.
US officials believe al-Qaida chief Usama bin Ladin and other senior al-Qaida figures are likely to be hiding in Pakistan's remote border areas. Pakistani officials say they do not know their whereabouts.