Two huge explosions were heard from Kirkuk airport Monday evening where a U.S. base is located, police sources said. Head of police operations Farhat Mohammed told Deutsche Presse- Agentur, dpa that the explosions were caused by two mortar shells that landed near the U.S. base. Smoke was seen rising from the area while sirens were heard throughout the northern Iraqi city. The U.S. base had not been targeted for a month. Meanwhile, Mohammed said that a police officer was killed by unknown assailants in the Rashid neighbourhood east of the city. --SP 2315 Local Time 2015 GMT