Nairobi - From hit and run attacks and massacres to a shopping trip, Somali-led al-Shabaab militants are on the march in northeastern Kenya.
With large numbers of troops in southern Somalia but seemingly unable to effectively police its own outer regions, Kenya must react quickly to stop the al-Qaeda-affiliated Islamists from gaining significant ground and finding a new generation of recruits, Western security officials say.
"The Somalia theatre is no longer of interest to the al-Shabaab," a Western security source told AFP.
"They've been defeated there. They are losing momentum, and their rare operations there don't get much media attention. It's the opposite in Kenya, where they have found a new playground for their jihad, a new source of recruits and a very strong potential to destabilise."
The upsurge in cross-border attacks and the emergence of Kenya-based al-Shabaab cells is now Kenya's number-one security headache, and a strategic blow given that it deployed troops into southern Somalia in 2011 in the hope they would serve as a buffer and protect the long, porous border.
Instead, Shebab units, hunted by African Union troops and US drones inside Somalia have flanked the Kenyan contingent to mount a string of gruesome cross-border raids.
In the Mandera region, aged 28 passengers were dragged from a bus and executed late last year. Days later, aged 36 quarry workers were pulled from their tents at night and murdered.
In Garissa, just half a day's drive from the capital Nairobi, a small group of gunmen stormed the town's university in April and massacred nearly 150 students during a day-long siege.
Filling the vacuum