Islamabad, Pakistan (CNN) The Pakistani Taliban have claimed responsibility for Tuesday's suicide attack which left at least 20 people dead in Peshawar, a city in the country's northwest.

Another 63 people were injured in the attack, according to Zulfikar Ali, the spokesman for Peshawar's Lady Reading Hospital. It is the deadliest militant attack in Pakistan this year and the first major attack as the country prepares for a general election on July 25.

In a statement, Pakistani Taliban (TPP) spokesman Mohammad Khurasani said that the "successful bombing (in Peshawar) is the beginning of revenge," and that "details of the suicide bombing will be shared soon."

The dead include Awami National Party (ANP) candidate Haroon Bilour, who was due to contest this month's election.

Bilour's father, former provincial minister Bashir Ahmed Bilour, was also killed in a suicide attack carried out by the Pakistani Taliban in 2012.

Pakistani security officials and volunteers search the site after a suicide bombing at an election rally in Peshawar on July 10, 2018.

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