One policeman was killed Tuesday when a bomb exploded in Kabul city, officials said. "A policeman was killed and three people injured in a blast in Pul-e-Yakpaisaghi in the inner city," said Khalil Dastiyar, deputy police chief in Kabul. The injured were two civilians and another policeman, he added. "We don't know who placed the bomb and for what purpose. An investigation is going on," Dastiyar said. Meanwhile, the Ministry of the Interior issued a statement condemning the attack by the "enemies of Afghan people." The police had discovered the bomb but it exploded while they were trying to defuse it, the statement said.