Several witnesses reported heavy troop movement in Kenya’s border regions, with truckloads of soldiers heading towards the frontier as military planes and helicopters overhead.
On Saturday Kenyan Internal Security Minister George Saitoti branded Somalia's Al-Qaeda-inspired Al-Shebab rebels "the enemy" and vowed to attack them "wherever they will be".
French woman Marie Dedieu was kidnapped from a beach resort 13 days ago, following a similar kidnapping of British woman Judith Tebbutt, while two female Spanish aid workers were seized by gunmen on Thursday.
Kenya already backs anti-Shebab and pro-government militia groups in Somali border regions in an attempt to create a buffer zone from hostile armed groups.
On Saturday, troops from Somalia's Western-backed government and allied militia wrested control of the Shebab-held town of Qoqani in the Lower Juba region on the Kenyan border.
Although Kenya blames the abductions on al Shebab, experts say the kidnappings could also be the work of pirates, bandits or criminal gangs.