The Somali armed Islamist group al-Shabab has seized a United Nations helicopter, along with about eight people, both passengers and crew, local sources have told the BBC.

The helicopter landed in territory controlled by the group in central Somalia.

Some reports said it had been forced to make an emergency landing, while others said the landing was a mistake.

Al-Shabab controls large parts of southern and central Somalia.

The group is affiliated to al-Qaeda and has waged a brutal insurgency since 2006.

The seizure of the helicopter was confirmed to the BBC by Galmudug region Security Minister Mohamed Abdi Adan.

The helicopter was heading to Wisil town near the frontlines of an offensive against al-Shabab by government forces when it landed.

The Somali government has in recent months intensified its fight against the al-Qaeda-linked group.

The UN has not yet commented.