|Shabab claimed responsibility for a car bomb in Mogadishu that killed more than 50 people on October 4 [EPA]
Kenyan troops have crossed the border into Somalia to fight rebel al-Shabab fighters they accuse of being behind several recent kidnappings of foreigners, Kenyan officials have said.
A military source told Al Jazeera on Sunday that the Kenyan troops were stationed about 100km inside Somali territory.
A reporter for the AFP news agency close to the border witnessed large numbers of troops as well as military planes and helicopters overhead.
Several witnesses reported heavy troop movement in Kenya's border regions, with truckloads of soldiers heading towards the frontier.
The assault comes a day after George Saitoti, Kenya's interior security minister, branded al-Shabab "the enemy" and vowed to attack them "wherever they will be".
Al-Shabab, or the "youth," are a hardline Islamic group that aims to overthrow Somalia's transitional government.