A suicide car bomber attacked an office used by Pakistan's main intelligence agency in the northwestern city of Peshawar on Friday, killing 10 people and wounding 60, officials said.
The city, near the Afghan border, has been targeted several times since the army began an offensive against the Taliban in South Waziristan last month and militants stepped up retaliatory attacks.
A military spokesman said the bomber's target was the office of the Inter-Services Intelligence (ISI) agency and the bomber detonated his explosives at a checkpost outside.
The attack came shortly before U.S. National Security Adviser Jim Jones began a series of meetings with military and government leaders in Islamabad.
The United States, weighing options as it struggles to stabilize Afghanistan, says Pakistani action against militants in border enclaves is vital for its Afghan effort.
The blast brought down the front of the three-storey building and sent a thick column of smoke billowing over the city.
A wounded soldier said the bomber was in a type of vehicle that usually delivers medical supplies.
"All of a sudden it appeared on the wrong side of the road and began coming toward the office," the soldier, Nasir, told Reuters. "The guards opened fire but it came to the entrance of the building as the firing went on and exploded."
It was not clear how many people were in the building when the bomber struck at about 6:40 a.m. (8:40 p.m. EST Thursday), before the city's rush-hour.
The ISI has in the past supported Islamists, beginning with guerrillas battling Soviet occupiers in Afghanistan in the 1980s, but in recent years has become a target of some militant factions.
Shortly after the Peshawar attack, a suicide car bomber attacked a police station near the northwestern town of Bannu, killing seven people including five policemen.
Bannu is a gateway to the North Waziristan, another major militant sanctuary on the Afghan border.
Security is tight across the country with numerous checks on roads and it was not clear how the bomber was able to approach the ISI office.
Militants who attacked army headquarters in Rawalpindi last month were dressed in army uniforms and traveled in a vehicle with military markings, reflecting an increasing sophistication in their attacks.
They were able to approach a gate of the sprawling headquarters complex but did not get through. Instead, they took hostages at a security office just outside the headquarters.
The army went on the offensive in South Waziristan last month, aiming to root out Pakistani Taliban militants behind a wave of violence in urban areas.
The militants have responded with intensified attacks in towns and cities, killing several hundred people.
Stock market investors have been rattled by insecurity and the main index has lost about 5 percent since the South Waziristan offensive was launched.
The main index opened lower but was 0.48 percent up at 8,967.07 at 0937 GMT in thin trade.
"Interest is lacking mainly because of such negative news," said Mohammed Sohail, chief executive at Topline Securities, referring to the Peshawar attack.
In Baluchistan province in the southwest of the country militants attacked tankers taking fuel to Afghanistan for international forces there, setting five ablaze and killing a driver, police said.