FOUR workers from Kenya's highways agency were killed in an ambush by suspected Islamist militants near the country's eastern border with Somalia, police said. The workers were leading a three-car convoy from the town of Garissa to Bura when they hit an explosive device planted in the road by suspected members of the Somali insurgent group al Shabaab, according to a police report. "A vehicle with four employees of the Kenya National Highway Authority was attacked with an IED, all the four died on the spot," said John Otieno, a local government administrator. Spokespersons for al Shabaab could not immediately…