The war, now in its seventh month, has killed more than 34,000 Palestinians, according to Gaza health authorities
At least 11 people were also wounded in the attack that took place soon after 2 am, 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.