(Updates death toll in lead, adds paras 2-5)
ISLAMABAD, October 1 (RIA Novosti) - At least 15 people, including four police officers, were killed and more than 20 injured in a suicide explosion in the town of Bannu in northwest Pakistan on Monday, police said.
At least seven of the injured are in a critical condition.
The blast went off in a crowded street when a suicide bomber in a rickshaw detonated an explosive device after approaching a group of policemen, local television reported.
No group has yet to claim responsibility for the attack, which comes just a few days before the country's presidential election, to be held on October 6.
Opposition parties have threatened to boycott the vote if the current president, Pervez Musharraf, runs for re-election.
