The Pakistani Taliban has claimed responsibility for three blasts targeting politicians, the latest in a series of

attacks meant to disrupt next month's parliamentary election, police said.

Eleven people were killed in Sunday's attacks.

In the first blast, a device exploded outside the office of an independent candidate in the garrison city of Kohat, which is adjacent to Pakistan's violence-plagued tribal areas along the Afghan border.

"The IED was planted outside the election office," Dilawar Khan Bangash. city police chief, said.

Ten kilogrammes of explosives were used in the attack, he said.

Violence has marred the campaign for the landmark May 11 election, with more than 50 people dead in blasts and suicide attacks since April 11, according to a tally by the AFP news agency, including more than 20 in the past three days.

Many of the attacks have been directed at candidates from secular parties opposed to the Taliban.

Fazal Naeem, a police spokesperson in Kohat, said the blast had damaged shops and vehicles near the office of Noor Akbar Khan and also hit an office of the Awami National Party, which has been threatened by the Taliban.

"The election office was open at the time and supporters of Noor Akbar Khan were sitting inside. The death toll may rise, the condition of some of the injured is critical," Tanveer Khan, another police official, said.

Rally targeted

Saifur Rehman, police officer, said the second bomb killed three at the office of another independent candidate, Nasir Khan Afridi, also running for a national assembly seat, in the suburbs of Peshawar.

The third attack occurred in the town of Swabi, where a bomb went off during a small rally held by the Awami National Party, which has been repeatedly targeted by the Taliban.

The blast killed two people and wounded five, said police officer Farooq Khan. The two candidates targeted in the attack, Ameer Rehman and Haji Rehman, were not hurt.

Al Jazeera's Kamal Hyder, reporting from Islamabad, said the bombings appeared to be part of a wider plan by the Taliban to create a climate of insecurity and sabotage the elections, and the group has been warning people not to go to the polls next month.

"The Taliban, it seems, are hell-bent on attacking targets across the country," he said.

On Saturday three blasts in Karachi, Pakistan's biggest city and commercial heart, killed at least three people and wounded 49.

Two of those bombs hit the offices of the Muttahida Qaumi Movement (MQM) and the Pakistan People's Party (PPP), which along with the ANP were coalition partners in the outgoing national government, led by the PPP.

The Pakistani Taliban has targeted the three parties, which are perceived as secular and backed military operations against the group.

As a result of the threats, there have been few large-scale political rallies leading to a lacklustre campaign for the elections.

Amnesty International has called on Pakistan to investigate the recent wave of attacks and ensure adequate protection for election candidates.