A roadside bomb in restive northwest Pakistan killed a political party official as he travelled to a campaign meeting on Sunday, a month before the country votes in a historic general election.

The blast in the Swat valley, which was ruled by the Pakistani Taliban during a 2007-9 insurgency, comes a day after militants blew up the office of an independent candidate in North Waziristan tribal district.

The attacks will fuel concerns that violence will mar the national and regional elections on May 11, which will mark the country's first democratic transition of power after a civilian government has served a full term in office.

Sunday's blast killed a local leader of the Awami National Party (ANP), which ruled the northwestern Khyber Pakhtunkhwa province from 2008 until assemblies were dissolved last month for elections.

"Mukarram Shah, a local leader of ANP, was travelling to Mingora when his vehicle was targeted by an IED (improvised explosive device), around 12 kilometres northeast of Mingora city," Gul Afzal Afridi, the district police chief told AFP.

Shah was alone in his car and no-one else was hit by the explosion.

There was no immediate claim of responsibility but the Pakistani Taliban have targeted a number of top ANP figures in recent months, assassinating the number two in the provincial government in December.

The militants claimed responsibility for a bomb attack on ANP rally on March 31 that killed two people and have warned they will strike again.