Eco-jihadism: Somali terror group al-Shabab ban single-use plastic bags
The announcement was made in a broadcast by Radio Andalus, an official mouthpiece of the militant group.
Mohammed Abu Abdullah, the group's governor for southern Somalia's Shabelle regions, said discarded plastic bags "pose a serious threat to the well-being of humans and animals alike".
Details of how the plan would be implemented would be announced soon, the broadcast said.
Al-Shabab also imposed an immediate ban on the logging of native trees, reported Huffpost, quoting a Somali website aligned with the group.
Al-Shabab, which is often referred to as "the deadliest" Islamist extremist group in Africa, is fighting to impose its hardline interpretation of Islamic law across Somalia.
A truck bombing by the group in October killed 512 people, the country's deadliest ever terror attack. Only a few attacks since 9/11 have killed more people.
The Horn of Africa nation continues to struggle to counter the militants. Concerns have been high over plans to hand over the country's security to Somalia's own forces, as a 21,000-strong African Union force begins a withdrawal that is expected to be complete in 2020.
The US military, which has bolstered its efforts against the militant group in the past year with dozens of drone strikes, has said Somali forces are not yet ready to take on the task themselves.
Experts say the move to join a global trend towards reducing the use of plastic products - which often make their way to oceans with devastating effects for marine life - is to show the group can govern.
Jihadi groups such as al-Qaeda and the Taliban have previously cited environmental issues in their propaganda.