Police in Tanzania say 20 Somali migrants suffocated to death during an attempt to smuggle them through the country.

They say the bodies of 17 men and three women were found along roads in Tanzania's Morogoro region between December 26 and New Year's Day.

Police say smugglers likely dumped the bodies one by one after the migrants died from lack of air while being transported in a truck, bound for Zambia.

Tanzania is increasingly a transit country for Somali migrants trying to reach South Africa. Thousands of Somalis flee their country each month, trying to escape years of recurring drought and chronic fighting.