12 police officers killed in Pakistan bomb blast

The explosion in the commercial hub of Karachi, which wounded almost 60 others, comes as Pakistan has been negotiating with the Taliban to end their seven-year insurgency that has claimed thousands of lives.

Senior police officials initially said the early morning blast was a suicide attack in which a small Suzuki van had smashed into the police bus.

But Raja Umer Khatab, chief of the city's counter-terrorism unit, later said the van had been parked on the hard shoulder along the bus's route and was remotely detonated when the two vehicles were side by side.

Shahid Nadeem Baloch, police chief for Sindh province which includes Karachi, confirmed the bomb was remotely detonated, adding the death toll was 12.

Doctor Semi Jamali at Karachi's Jinnah hospital said 58 people were injured -- both police on the bus and civilian passers-by. Nine of the injured police were in critical condition.

The attack happened in an eastern district of Karachi near the national highway.

Syed Qaim Ali Shah, chief minister of Sindh, announced compensation of two million rupees ($20,000) for families of the victims, and free medical treatment for the injured.

- 'Revenge' attack -

Tehreek-e-Taliban Pakistan (TTP) spokesman Shahidullah Shahid told AFP it was a revenge attack for the killing of militants.

"We carried out the attack against the police because they are killing our people," he said over the telephone from an undisclosed location.

"Our defensive war will continue until an agreement is reached on a ceasefire" between negotiation teams representing the government and the Taliban.

The Pakistani Taliban have recently stepped up their campaign against security forces in Karachi, assassinating a so-called "super cop" Chaudhry Aslam earlier this year.

The attack was the 11th since Prime Minister Nawaz Sharif announced talks on January 29 and said he wants to "give peace another chance".

Provincial officials vowed the bombing would not deter their campaign to root out criminals and terrorists.

"We are investigating this attack from all angles ...The forces will not be demoralised and will work more aggressively," said Sharjeel Memon, provincial information minister.

Karachi, a city of 18 million people which contributes 42 percent of Pakistan's GDP, has also been plagued for years by sectarian, ethnic and political violence.

- Bloody start to year -

Pakistan has endured a bloody start to the year with 114 people killed in attacks in January, according to an AFP tally.

More than 60 people have died in Islamist-linked violence since Sharif announced the talks.

On Wednesday militants stormed a house of anti-Taliban activists and shot dead nine men in the northwestern city of Peshawar.

On Tuesday a triple grenade attack on a cinema showing pornography in Peshawar killed 13 people.

Both government and militants says they are serious about peace talks but analysts remain sceptical about their chances of success.

Past agreements between the Taliban and the army have proved to be short-lived.

In 2009 the army launched a full-fledged offensive in the northwestern hilly region of Swat, after a two-year local peace deal with the Taliban broke down there.