Kenya's police commissioner is warning owners of shopping centers and hotels to be vigilant after threats by a Somali militia group that has already carried out one international attack.

Mathew Iteere said Monday that police have increased security in public areas in response to Sunday's threat from the Somalia-based al-Shabab militant group.

Al-Shabab spokesman Sheik Ali Mohammed Rage said Kenya "would pay" for allegedly helping Somali government troops and their allies attack the militants' bases in Somalia.

Al-Shabab — Somalia's most dangerous militant group — claimed responsibility for the double suicide bomb attack in Uganda's capital in July during the World Cup final. The blasts killed 76 people.