At least one policeman was killed and four others were injured Sunday morning after sticky bombs attached to a police vehicle detonated in Yemen\'s southern port city of Aden, a police official told Xinhua. According to the local official, a car bomb exploded beneath the policemen vehicle, killing at least one policeman and injuring four others. \"The police vehicle stationed near Aden\'s International Airport exploded after terrorists planted an explosive device in the car,\" the official said, adding that \"the policemen were in charge of guarding the airport.\" An eyewitness said that the explosion was \"powerful.\" Sunday\'s attack came two days after the head of counter- terrorism force in Aden was killed in a car bombing in a main street near the Aden\'s International Airport. A number of intelligence offices and police stations in Aden have repeatedly been the targets in the past several months. Yemeni authorities usually accuse militants of the al-Qaida in the Arabian Peninsula (AQAP) of being behind these attacks. In nearby Abyan province, hundreds of AQAP militants captured in the provincial city and at least three towns late May. Meanwhile, the country has been gripped by nine-month political crisis since protests erupted in late January demanding an immediate end to President Ali Abdullah Saleh\'s 33-year rule.