ISLAMABAD, July 30: Strict enforcement of travel restrictions on diplomats based in Pakistan has escalated tensions with the United States and the issue is threatening to turn into another major diplomatic spat between the two.

For now the two are, for the second time this year, wrangling over the interpretation of Vienna Convention on Diplomatic Relations 1961 (VCDR), which governs diplomatic ties between countries.

Although the Foreign Office had notified all diplomatic missions, including the US, in June that diplomats would require a no-objection certificate (NoC) while travelling to other parts of the country, things came to a head when Ambassador Cameron Munter was stopped at Benazir Bhutto Airport Islamabad and asked for the document permitting his travel to Karachi.

Ambassador Munter, who was reportedly in possession of the document, took strong exception to having been asked about the NoC and strongly protested over the incident. The issue was then taken up with President Zardari.

The incident occurred earlier this week when the ambassador was travelling to Karachi. He was initially scheduled to visit Karachi on Tuesday, but the trip was put off for two days. The US consulate in Karachi had said at the time that the change in the ambassador’s itinerary was made for reasons of health.

The Americans see the NoC requirement as a violation of Article 26 of VCDR, which obligates the host stateto “ensure to all members of the mission freedom of movement and travel in its territory”.

However, Pakistani officials contest the US embassy’s view saying under VCDR movements could be regulated for national security purposes.

Foreign Office in a rejoinder to the US claim said: “Pakistan is fully mindful of its obligations under the Vienna Convention on Diplomatic Relations.”

The FO statement further denied that the curbs were US specific insisting that the requirement was for security of the diplomats.

“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,” the statement explained.

Pakistani officials in their interactions with the US officials have tried to play down the travel regime telling their interlocutors that it was “preventive rather than restrictive”.

Both the US and Pakistani officials said they were working to resolve the issue.

A security official, speaking on the background, said the restrictions were enforced because of the travel of under-cover foreign intelligence agents, who have been assigned to Pakistan as diplomats.

Even if, he did not explicitly say the checks were meant to counter the movement of the CIA officials, but it wasn’t difficult to judge from his conversation that it about CIA personnel, who they believe were still operating without coordination with ISI despite revised terms of engagement of the two agencies.

CIA’s footprint in the country was cut down after the May 2 raid on Osama bin Laden compound in Abbottabad, but number of its (CIA) agents were issued visas after the two spy agencies reworked their relationship and the US intelligence agency agreed on greater transparency about its operations inside Pakistan.

Background discussions with officials at Foreign Office suggested that they realised that holding up Ambassador Munter was a little too much and that they were contemplating a review of the NoC requirement for exempting the heads of missions in order to prevent such embarrassing incidents from recurring.