NAIROBI, Kenya - At least four people were killed Saturday after a device exploded inside a passenger van in the capital, Kenyan police said, in what appears to be the first attack inside Nairobi since the deadly terrorist assault on an upscale mall in September.

The explosion happened as the minibus was traveling from Eastleigh neighborhood of Nairobi to the city center, said Benson Kibue, chief of police in Nairobi. Investigators believe an improvised explosive device was used in the Saturday attack that injured at least 25 others, he said.

Sometimes called Kenya's "Little Mogadishu," Eastleigh is known for its large population of ethnic Somalis. The neighborhood came under fresh scrutiny by investigators after the Sept. 21 attack on Nairobi's Westgate Mall, a bloody four-day siege in which at least 67 people were killed.

A Western official familiar with the Westgate attack investigation told the Associated Press last month that all four attackers were ethnic Somalis who had spent time in Eastleigh.

Kenya has been the scene of multiple terrorist attacks since the country sent its military to Somalia in 2011 to fight the extremist Somalia militant group al-Shabab.