NAIROBI - Unidentified gunmen killed at least 13 people in Mandera, a town in northeastern Kenya early on Tuesday, the head of the Kenya Red Cross was quoted as saying on Kenyan television.At least 11 people were also wounded in the attack that took place soon after 2 a.m. (2300 GMT), the Kenya Red Cross also said on its Twitter feed."(There are) 13 people who are dead. We know there are 11 that are injured," Abbas Gullet, secretary general of the Kenya Red Cross, told Citizen Television.Gullet said four of the injured would be evacuated to the capital, Nairobi, medical treatment."This (is) ... what we understand, (they) were quarry workers. They were sleeping when they were attacked early hours of this morning," Gullet said.