The UN has warned of a severe outbreak of polio in Somalia, days after a medical charity pulled out of the country, citing insecurity, BBC News reported.

At least 105 cases of polio have been recorded in Somalia this year - almost half the number of cases around the world in 2012.

The World Health Organization is trying to eradicate polio and the number of cases has fallen dramatically. Most of the Somali cases are in areas controlled by Islamist group al-Shabab.

Polio is now only considered endemic in three countries - Afghanistan, Nigeria and Pakistan. Somalia was declared polio-free six years ago and some four million people have been vaccinated.

The BBC's international development correspondent Mark Doyle says in many parts of Somalia the charity is the only provider of health care ranging from basic medical supplies to major surgery.

Some 18,000 African Union troops are in the country supporting the UN-backed government - the first one in more than two decades to be recognised by the US and the International Monetary Fund (IMF).

The Islamist al-Shabab militant group no longer has bases in Mogadishu and has also been pushed out of other cities.

But it remains in control of smaller towns and large swathes of the countryside in central and southern Somalia and continues to launch occasional suicide attacks.