(CNN) -- At least six people were killed and some 18 were wounded by an explosion in what appears to be a "deliberate attack" in Nairobi, Kenya, a senior Red Cross official tells CNN.
Nine of the injured were listed in critical condition at Kenyatta National Hospital, the Kenya National Disaster Operation said on its Twitter account. The other wounded people were treated "locally," the agency said.
"Our resolve & will to defend ourselves from those who intend to harm us will never be discouraged," the governor of Nairobi City County, Evans Kidero, said in a tweet. "Our strength lies in our national unity."
The explosion occurred in Eastleigh, a largely Somali neighborhood, east of the Nairobi city center.
Authorities have not said what caused the blast.
CNN's Joseph Netto contributed to this report.