At least 24 people have been killed and 100 injured in two suspected suicide car bombings in the city of Lahore in eastern Pakistan.
A majority of the victims died in a car bomb attack that hit a federal police building in the heart of the city.
Another bomb in a suburb killed three, including two children, police say.
Shortly after the blasts, the Australian cricket team announced the cancellation of their forthcoming tour of Pakistan over security fears.
The police said the first explosion hit the Federal Investigation Agency (FIA) at 0925 (0425 GMT) in Lahore.
It demolished part of the building, where about 250 people work, just as employees were beginning their day.
The remainder of the building was evacuated as rescue workers struggled to remove the wounded from the debris.
The second, near-simultaneous blast hit an office in a residential district of Lahore several miles away, killing three people, including two children.
President Pervez Musharraf said: "Acts of terrorism cannot deter government's resolve to fight the scourge with full force."
Suicide attack probe
One witness who was inside the police building at the time of the blast described what he saw.
"There was a huge explosion and I fell down senseless," said FIA employee Ali Ahmed.
"For a moment, I didn't know if I was dead or alive. When I finally came to my senses, I was able to locate a window and crawl out."
A man who works within walking distance of the building described the intensity of the explosion.
It "was so huge that nearby buildings were shattered and we witnessed huge clouds of smoke and dust rising to the sky", Muhammad Raza told the BBC.
The bombs have deepened Pakistan's security crisis
"It felt like the aftershocks of an earthquake."
At least 12 of the dead were FIA officials, says the head of the FIA's investigation wing, Tassaduq Hussain.
Many of the injured included children from nearby schools.
At the time of the bombing, military officials in the building were investigating a 4 March suicide attack at a nearby naval college, the head of the FIA in Lahore, Mian Manzoor, told the BBC.
The country has been hit by a wave of suicide bombings in the past year, most against security targets, says the BBC's Barbara Plett in Islamabad.
It is rare for groups to claim responsibility for the attacks, but they are usually blamed on pro-Taleban militants and on elements of now banned jihadist groups nurtured by the intelligence agencies.
They are believed to be in response to army and police operations against the militants.
Most take place in the north-west of the country near the Afghan border, but many of Pakistan's major cities have also been hit.
Former Prime Minister Benazir Bhutto was killed by a suicide bomber in Rawalpindi in December.
Until recently Lahore had escaped the violence, but there have been three attacks there now in the last two months.
Four people died in last week's attack on the naval college. And in January, 19 people were killed in a suicide bombing near the High Court.
More than 500 people have been killed in the country since the beginning of the year in a campaign of attacks and bombings blamed on Islamist militants.