US ambassador stopped at Islamabad airport; asked about NoC ISLAMABAD: The US lodged a strong protest with Pakistani authorities after ambassador Cameron Munter was stopped at the airport here by officials enforcing a rule that requires all foreign diplomats to have a "no-objection certificate" for travelling outside Islamabad. Munter, who reportedly possessed the NoC, was stopped at Benazir Bhutto International Airport and asked about the document while he was travelling to Karachi last week. The envoy "strongly protested" about the incident, which was subsequently taken up with President Asif Ali Zardari, the Dawn newspaper reported. The incident reflected the tensions that have characterised US-Pakistan relations since al-Qaeda leader Osama bin Laden was killed by American special forces in a covert raid in Abbottabad on May 2. Pakistan had threatened to impose "more formal restrictions" on travel by all US diplomats and to require prior notification but dropped the demand when the American administration threatened similar restrictions for Pakistani diplomats in the US, an unnamed US official was quoted as saying by ABC News. Pakistan's Inter-Services Intelligence began keeping a close watch on American diplomats in the wake of the raid against bin Laden as it believed the CIA was running a secret network of American and Pakistani operatives in the country. The foreign office sought to play down the incident involving Ambassador Munter, with spokesperson Tehmina Janjua saying "no US-specific" travel restrictions had been applied. "However, there are general guidelines regarding travel of Pakistan-based diplomats, designed only to ensure their safety and security, which have existed for a long time," she said in a statement.