A bomb attack on the convoy of a ruling party politician in northwest Pakistan killed five policemen and wounded four others on Sunday, officials said.The incident took place in the Martoong area of Swat valley, which the Taliban controlled from 2007-2009, as the convoy of Amir Muqam, an adviser to Prime Minister Nawaz Sharif, passed through."At least five policemen were killed and four others were wounded," senior police official Abdullah Khan told AFP.The dead and wounded were travelling in the security car that was leading the convoy, he said, adding that police were investigating the precise circumstances of the blast.Another senior police official, Gulzar Khan, confirmed the attack, which was later condemned in a statement by the prime minister's office.Muqam told AFP that he was safe but distraught over the loss of the men in his security detail."I thank God for saving my life. I am very sad over the loss of my people who gave their lives while protecting me," he said.He said that he was travelling in the area with some 15 vehicles in his convoy as part of campaign efforts for local elections."This is not the first attack on me. This is the sixth attack, but I will not be deterred from carrying out my political activities," he added.Later, talking to a private news channel Muqam said that he saw the debris of the pilot car and pieces of human flesh falling from it.Muqam did not name who he thought was behind the bombing, but said that "There are people who cannot tolerate the truth and they want to silence the voice of the truth."In July 2011, a suicide bomber killed six people including a child in Swat valley where Muqam was to address a public meeting.