Meanwhile, the country remains in shock in the wake of its deadliest terrorist attack.
At the bomb site, local television reports that Pakistan teams have been joined by three American investigators scouring the ruins for evidence.
Forensic teams will also be scrutinizing hotel security video that shows the explosives-packed truck ramming - unsuccessfully - the hotel barrier.
Minutes tick by - until at last the suicide bomber in the cab detonates a small explosion.
A brave guard tries to put the fire out, then gives up … then the main blast that destroyed the hotel, killing 53 people, including two U.S. Marines attached to the American embassy and the Czech ambassador to Pakistan.
A third American - a contractor for the State Department - is reported still missing.
We've learned that all three American schools in Pakistan have been closed for the rest of the week after receiving threats.
British Airways has confirmed it has suspended some of its flights to Pakistan while it reassesses the security situation.
Change Of Plans Saved Pakistani Leaders From Blast
Pakistan's top leaders were to dine at the Marriott hotel that was devastated by a truck bombing over the weekend, but changed the venue at the last minute, a senior government official said Monday.
Interior Ministry chief Rehman Malik did not specify why the prime minister and president decided to move the dinner from the Marriott to the premier's house but said the decision was kept secret.
"Perhaps the terrorists knew that the Marriott was the venue of the dinner for all the leadership where the president, prime minister, speaker and all entire leadership would be present," he told reporters. "At the eleventh hour, the president and prime minister decided that the venue would be the prime minister's house. It saved the entire leadership."
Some 270 people were wounded in the attack, while the dead included the Czech ambassador and two U.S. Department of Defense employees.
Most of the victims were Pakistanis, a fact likely to increase pressure on the government to stem the rising violence in the Muslim nation that many blame on the country's partnership with the U.S. in the war on terror.
Suspicion has fallen on al Qaeda or the Pakistani Taliban in the blast.
But Amir Mohammad, an aide to one prominent Pakistani Taliban leader, Baitullah Mehsud, said the militant group was not involved and shared the nation's grief. Mehshud was blamed by the last government for a suicide attack that killed Pakistan President Asif Ali Zardari's wife, the pro-U.S. politician Benazir Bhutto. He denies that charge, too.
"We have our own targets and we execute our plans precisely with minimal loss of irrelevant or innocent people," Mehsud was quoted as saying by his spokesman. "We have nothing to do with the Marriott hotel attack."
The government is under U.S. pressure to crack down on the militants, who are also blamed for staging rising attacks on coalition forces in neighboring Afghanistan.
U.S. Helicopters Fired Upon After Entering Pakistan Airspace
Two intelligence officials said Pakistani troops and tribesmen opened fire on two U.S. helicopters after they crossed from Afghanistan into the northwest tribal region, where Taliban and al Qaeda militants are operating.
The officials who described Monday's helicopter incursion into the border region spoke on condition of anonymity because they were not authorized to speak to the media. They said informants in the field told them it took place about one mile inside the disputed and poorly demarcated border in the Alwara Mandi area in North Waziristan.
The helicopters did not return fire and re-entered Afghan airspace without landing, the officials said.
Pakistan's army and the U.S. military in Afghanistan said they had no information on the reported incursion.
A week ago, U.S. helicopters reportedly landed near Angoor Ada, a border village in South Waziristan, but returned toward Afghanistan after troops fired warning shots.
The alleged incident will likely add to tensions between Islamabad and Washington and comes as Zardari heads to New York to attend the U.N. General Assembly.
In a further sign of the country's deteriorating security situation Monday, gunmen kidnapped Afghanistan's ambassador-designate and killed his driver in the main northwestern city of Peshawar, said a spokesman for the mission in the city.
The spokesman, who gave his name as Babri, said Abdul Khaliq Farahi was abducted as he traveled toward his home in the city. He gave no more details, but the kidnapping and killing was also confirmed by the Afghan charge d'affairs in Islamabad, Majnoon Gulab.