Al-Shabaab spokesman Sheik Ali Mohamud Rage threatened Kenya with reprisal after hundreds of Kenyan infantry, assisted by tanks and helicopters crossed the border into Somalia Sunday, al-Jazeera reported Monday.
The Kenyan government has ordered the troops to pursue the al-Shabaab guerrillas who they say are responsible for the recent kidnappings of a French tourist, two Spanish aid workers and a British tourist whose husband was fatally shot.
"Kenyan troops have entered 100 kilometers (62 miles) into Somalia and their planes bombarded many places and killed residents. We shall come into Kenya if you do not go back," Rage said.
The Somalia government has approved Kenya's raid, al-Jazeera said.
(Kenya) "has a right to defend its people," Nur Ahmed, the Somali ambassador in Nairobi, said.
In Somalia, a radio station controlled by al-Shabaab asked Somalis if they were ready to "live under Christians" and urged them to fight.
Kenya's defense ministry did not comment.