Denmark's prime minister, Helle Thorning-Schmidt, said the country was on high alert after a "terrorist attack" in Copenhagen that police said had been aimed at a controversial Swedish artist."We feel certain now that it was a politically motivated attack, and thereby it was a terrorist attack," she told reporters close to the site of the shooting, in which one civilian was killed and three policemen were wounded. "We are on high alert all over the country."Police said preliminary interviews with witnesses suggested there had been only one attacker, not two as they had previously stated, and issued a photograph of the suspect.