A curfew was imposed in South Wazaristan on Saturday, ahead of any offensive.

Mohammad Khalid Khan, a senior government official, said: "The curfew is for the protection of military convoys [moving toward Taliban strongholds] and it is on the roads. The bazaars are opened."

The government said on Friday that a ground offensive against the Pakistani Taliban in South Waziristan was imminent and the army has been stepping up its air and artillery attacks in recent days to soften up their defences.

Pakistani forces attacked the Taliban in South Waziristan on the same day with aircraft and artillery.

US hopes

The US hopes that a Pakistani army operation in South Waziristan will help break much of the opposition network that threatens both Pakistan and American troops across the border in Afghanistan.

In depth

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The Pakistani military has reportedly already sent two divisions totalling 28,000 men and blockaded the area. Analysts say that with winter approaching, any push would likely have to begin soon to be successful.

Saturday's reports of a decision on an offensive came a day after at least 11 people died in two explosions near a police office in the city of Peshawar.

The bombs were detonated at an investigation bureau in an army garrison of the city, Asghar Hussain, a police official, said.

The strikes were the latest in a series of attacks that have killed more than 150 people in Pakistan over the past two weeks.

Local police said one of the attackers was a woman, making it the second time that a female suicide bomber has attacked in Pakistan.

Attack investigation

"Police tried to intercept a woman sitting on a motorcycle with a terrorist. She blew herself up and after that there was another blast when a suicide attacker sitting in a car exploded," Liaqat Ali Khan, the city police chief, said.

"An attack had happened here already once before ... We don't feel secure here, we don't know when it will happen again," Allah Ditta, a local resident, said.

Hasan Askari Rizvi, a political and defence analyst, said: "Different terrorist groups are now trying to reassert themselves, because after the [Pakistani army] Swat operation and the death of Baitullah Mehsud, [the leader of the Pakistani Taliban] the impression was that they were in disarray.

"Now they want to demonstrate they are capable of taking action in any part of the country.

"They want to deter [security forces] from taking action in South Waziristan where action is expected against the Taliban."

Also on Friday, police said dozens of people had been picked up in overnight raids in slum areas of Lahore and neighbourhoods populated by Afghans, a day after 40 people died in a string of attacks on security buildings in Lahore and bombings in the northwest.

"There has been considerable progress in the ongoing investigation. We have arrested dozens of suspects during overnight raids in Lahore," Haider Ashraf, senior police official at the  Manawan police academy, told the AFP news agency.

"These people are being interrogated. We are also trying to identify the terrorists who were killed yesterday," he said.