YAOUNDE (Reuters) - Eleven hostages from Cameroon were freed on Sunday following 16 months of captivity, after having been abducted by a militia group from the Central African Republic, a statement from the Cameroonian presidency said.

The hostages included a local mayor, Mama Abakai, and 12 others, but two died in captivity, said President Paul Biya in the statement, adding that the crime would not go unpunished.

It was not clear which militia abducted them or how they were freed.

They were kidnapped in March 2015 by heavily armed men while returning from a funeral in Cameroon's northern Gbabio district, and taken over the nearby border to the Central African Republic.

"The Cameroonian hostages were freed today and they are en route to Yaounde," Governor Grégoire Mvono told Reuters.

An upsurge of violence in the Central African Republic that began in 2013 has caused thousands to flee across the border and increased insecurity in parts of Cameroon.

Islamist militant group Boko Haram has also staged numerous cross-border attacks from Nigeria into Cameroon's Far North Region. 

(Reporting by Josiane Koaugheu; Writing by Matthew Mpoke Bigg; Editing by Andrew Bolton)