A British newspaper claimed that the US is pressurizing Pakistan to release Dr Shakil Afridi. According to the Guardian, the Washington is pressing Islamabad to release a doctor being held for helping the CIA track down Osama bin Laden as the diplomatic falling-out between the countries grows more bitter. Dr Shakil Afridi was arrested by Inter-Services Intelligence (ISI) agency after it discovered he had been recruited by the CIA to run a fake vaccination programme in Abbottabad to try to get DNA samples from the al-Qaida leader's suspected hideout. American authorities are trying to rescue the Pakistani doctor, his wife and children, and take them to the United States, according to Pakistani and US officials. The revelation that Bin Laden was living comfortably in northern Pakistan and the clandestine operation by US special forces to kill him on 2 May have pushed ties between Washington and Islamabad to breaking point. Over the weekend, the US announced that it would punish Pakistan for its lack of co-operation in the anti-terror fight by cutting $800m (500m) in military aid. In retaliation, Pakistan's defence minister on Tuesday threatened to pull out over 100,000 troops posted on its side of the border with Afghanistan, which would be a security disaster for the coalition's ongoing military campaign. The recruitment of Afridi has added to the tensions. The doctor, in his late 40s, is thought to have been detained in late May or early June, and is not thought to have been charged. He is being held for working for a foreign intelligence agency, which can be punishable by the death penalty. Friends say they last saw him attend the funeral of a distant family member in Peshawar, the provincial capital of the north-west, on 18 May. Afridi worked as the doctor in charge of Khyber, part of the tribal area, on the edge of Peshawar. It is believed that he was snatched by the ISI at Karkhano bazaar, a market for smuggled goods, on his way back home to Peshawar from work in Khyber, that lies between Peshawar and Khyber. He was initially held in custody in Peshawar, but may have been transferred to custody in Islamabad. From a humble family, Afridi graduated in 1990 from Khyber Medical College, the top medical academy in the north-west of the country. He had been accused of corruption in the past but was cleared of misdoings, according to one person who knows him. The CIA was never sure that Bin Laden was hiding inside the house in Abbottabad, northern Pakistan. It recruited Afridi, who set up a fake vaccination programme in Abbottabad. It was hoped that this would produce a DNA sample from one of the Bin Laden children. A nurse working for the doctor managed to get inside the compound, though it is not thought that the right DNA was obtained. The Guardian revelations about the fake CIA vaccine programme made headline news in Pakistan on Tuesday, but government officials offered no comment. Already chilly US-Pakistan relations grew colder in recent days with the news that Washington is to withhold $800m of military aid. Much of that money would have gone toward reimbursing Pakistan for the costs of keeping over 100,000 troops in the tribal area, guarding the border with Afghanistan, under a scheme known as Coalition Support Funds. "This is money we have already spent on this war," Ahmad Mukhtar, Pakistan's defence minister, said in an interview with Express 24/7, a Pakistani news channel. "The next step is that the government or armed forces will remove these soldiers from the border." According to figures released by the US Congress, Washington has paid Pakistan $8.9bn in Coalition Support Funds since 2001. The money is meant to pay for the costs of maintaining the Pakistani troops in the tribal area. Pakistan's armed forces are accused of allowing militants to sneak across the border from safe havens in the tribal area to carry out attacks in Afghanistan. However, Pakistan says it maintains 1,100 border check posts and does its best to stop the flow. If those posts were removed, the Taliban would be able to pour across unhindered. But Mukhtar's comments are likely to be a warning shot, as pulling out those troops from the tribal area would create a huge security threat for Pakistan too.