Pakistani and US intelligence officials say a weekend bomb attack in Pakistan bore the hallmarks of an operation by al-Qaeda.
At least 53 people were killed and hundreds more were wounded in the blast at the Marriott Hotel in the capital, Islamabad.
The truck used in the attack was said to have been packed with 600kg of high grade explosives.
Pakistan's government says it will take targeted action against militants.
A senior Interior Ministry official, Rehman Malik, said raids would be carried out in what he called hotspots near the Afghan border.
Islamabad police chief Asghar Raza Gardezi said no arrests had been made in connection with the blast and declined to give any details about the hunt for evidence.
British Airways has suspended its flights to Pakistan because of security fears, an airline spokesman said.
Last night, Pakistani security forces opened fire at two US helicopter gunships which violated Pakistani airspace in a tribal region bordering Afghanistan.
The helicopters violated the border in the area of Lowara Mandi, 80km west of Miranshah, the main town in the North Waziristan tribal region, according to reports. There has been no official confirmation.
Relations between the US and Pakistan became frayed earlier this month after US commandos raided a border village in South Waziristan and killed 20 people, including women and children.
