At least 20 people were killed by two bombs that ripped through a federal police headquarters and an advertising agency in the Pakistani city of Lahore on Tuesday, police said.
The blasts were the latest in a wave of violence across Pakistan that has left more than 600 people dead this year and posed a serious challenge to an incoming coalition government that won elections on February 18.
The first attack demolished part of the federal investigation agency (FIA) office in the eastern Pakistani city, exposing the inside of the building and leaving piles of blackened rubble and burning cars.
"Sixteen people were killed in the blast that took place in FIA premises. It seems that a bomb was planted somewhere in the building," local agency chief Chaudhry Manzoor Ahmed told AFP.
However a police investigator said that the blast was a suspected suicide attack.
"We believe the suicide attacker came in a vehicle and hit the reception counter. We have recovered only a few pieces of the car which was used in the attack," investigations superintendent Babur Bakht Qureshi told AFP.
Pools of blood and small pieces of human flesh lay scattered on the ground outside the eight-storey building, along with clothes and pairs of shoes that were abandoned by people as they ran away, an AFP reporter said.
Police cordoned off the area while emergency workers carrying stretchers scrambled over the rubble. A car was set ablaze by the force of the blast and others were covered in downed electricity cables and rubble.
The building was evacuated because of fears it could collapse, television channels reported.
The second near-simultaneous blast hit an advertising agency in an upscale neighbourhood of the city killing another four people, Qureshi said. He said there were no further details.
The latest explosions came a week after two suicide bombers blew themselves up at a prestigious naval college in Lahore, killing at least five people and wounding 19, officials said.
The city, close to the Indian border, had previously seen little of the violence that has rocked other Pakistani towns, although it also suffered a major suicide bombing in January that killed 20 people, mostly police.
Pakistan has been rocked by six major blasts since the February 18 polls, which were won by the parties of slain ex-premier Benazir Bhutto and former prime minister Nawaz Sharif.
The parties at the weekend signed an agreement on forming a coalition government.
Pakistan has been combating an Islamist insurgency led by Al-Qaeda and Taliban fighters since President Pervez Musharraf joined the US-led "war on terror" in 2001, but the violence has soared since the start of 2007.
Around 600 people have died since the start of this year in suicide attacks, roadside bombings and clashes, mainly along the Afghan border in troubled northwestern Pakistan but also in major cities.
Many of the attacks have targeted the armed forces, police and security forces.
The army's top medical officer, Lieutenant General Mushtaq Baig, was killed in a suicide attack in the garrison city of Rawalpindi on February 25. (AFP)
Twin bombs kill 20 in Pakistan's Lahore