At least 27 persons were killed on Tuesday in Kenya when an oil tanker collided with a bus on the Nairobi-Mombasa highway, authorities said.The bus was travelling to Nairobi when it hit the tanker near Makindu in Kibwezi, Xinhua news agency quoted police commander Leonard Kimaiyo as saying."We have lost many people and others are critically injured," he said, adding that the death toll was expected to rise.According to him, the bus driver was trying to overtake other vehicles when it collided with the tanker.Kenya ranks first in African countries with the highest toll of road accidents caused due to speeding and poor enforcement of traffic rules.According to government statistics, Kenya loses over 3,000 people annually in road accidents.