Pakistan has imposed an economic blockade on the mountain stronghold of Baitullah Mehsud, the leader of the Pakistani Taleban, in an effort to turn his tribesmen against him and encourage civilians to flee before a planned ground offensive, according to local officials.

Authorities are also arresting dozens of Mehsud tribesmen and shutting down the businesses of others on the fringes of South Waziristan — thought to be the hiding place of Osama bin Laden — under a draconian “collective responsibility” law which was introduced in the British colonial era.

Britain imposed the Frontier Crimes Regulations (FCR) in 1901 in an effort to control the local Pashtun tribes, whose strict honour code obliges them to give sanctuary to anyone who requests it, including, since 2001, many Afghan Taleban and al-Qaeda leaders.

Under the regulations, which are still in force in Pakistani tribal areas, the Government can punish an entire tribe that refuses to hand over a wanted person by detaining its members, fining them and confiscating or destroying their property.

A local intelligence official told The Times that the army had blocked all three main roads leading to Mr Mehsud’s territory in South Waziristan and allowed only civilians to leave the area. A member of the Mehsud tribe in the town of Tank, close to South Waziristan, said that his store and dozens of others owned by Mehsuds had been sealed under the FCR. “If the Government can’t get control of Baitullah and his men, then how can they put pressure on us poor people to control them?” he asked.

Maulana Saleh Shah, a senator and prominent local cleric, told a jirga, or tribal council, in Tank that an estimated 100,000 people had fled South Waziristan in the past few days. Muhammad Anwar, a student in Tank, said: “There is a sense of complete fear everywhere. The whole Mehsud tribe is being punished because of a small group of militants.”

South Waziristan is the biggest of Pakistan’s Federally Administered Tribal Areas, with a population of about 500,000, most of whom belong to one of two tribes, the Mehsuds and the Wazirs.

Mr Mehsud is said to command 10,000 men from his tribe and has forged a loose alliance with two Waziri commanders — Mullah Nazir in South Waziristan and Hafiz Gul Bahadur in North Waziristan.

The Government now has the support, however, of two rival Mehsud leaders, Qari Zainuddin and Turkistan, and is negotiating with Mullah Nazir and Hafiz Gul Bahadur.

The blockade is designed to isolate Mr Mehsud further as the army prepares for the offensive by pummelling his territory with artillery and airstrikes and moving troops and armour towards the region.

Critics say that it risks antagonising tribesmen, who already endure the highest rates of unemployment and lowest living standards in Pakistan as well as regular military operations and missile strikes from American drones.

They also warn that while some tribesmen may turn against Mr Mehsud, many continue to support al-Qaeda and the Taleban, and will resist any attempts to impose central government control or curb incursions into neighbouring Afghanistan.

“If the intent is to dissuade people from supporting the insurgents, then they’ll only end up creating more unhappiness and feeding the insurgency,” Samina Ahmed, South Asia project director for the International Crisis Group, said. “This is a bad law that the British left behind and it continues to treat local people like colonial subjects,” she said. “It hasn’t worked in the past and there’s no reason to think it will work now.”

US and British officials have so far welcomed the planned attack on South Waziristan, as they have been pressing the army for years to capture what they see as al-Qaeda’s main regional hub. Some are concerned that the attack will overstretch the army, which has yet to complete the operation it launched in the northwestern region of Swat in April and still faces sporadic fighting in the tribal regions of Bajaur and Mohmand.

Others fear that the Pakistani Army will withdraw from South Waziristan after killing or capturing Mr Mehsud and avoid confronting other militant leaders seen as a threat to American and Nato troops in Afghanistan but not to Pakistan.

Aid workers worry that the operation could cause heavy civilian casualties and up to half a million more refugees to add to the 2.5 million who have fled the fighting in the northwest in the past year.

Brad Adams, of Human Rights Watch, warned: “The Taleban’s disregard for civilian life should not be mimicked by the Pakistani military. For warnings of impending attacks to be effective in reducing civilian casualties, the army needs to allow civilians time to evacuate and recognise that not everyone will be able to leave.”

South Waziristan was high on the agenda yesterday when President Zardari made a rare trip to Nato headquarters in Brussels and attended an inaugural summit with EU leaders.

Nato commanders were expected to discuss plans to launch parallel operations on the Afghan side of the border with South Waziristan to prevent Mr Mehsud and his men from fleeing to Afghanistan.

The EU used the summit to pledge €65 million (£55 million) in humanitarian aid for the refugees from the fighting. It did not comply with Mr Zardari’s request for closer commercial ties to help to rebuild his country’s war-ravaged economy.

“What I need is trade, not aid,” he said.

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