Yemeni ex-president Ali Abdullah Saleh is suspected of corruptly amassing as much as £40 billion, equivalent to Yemen's annual GDP, during his long rule, and colluding in a militia takeover last year, UN-appointed investigators have told the Security Council.

The report by the world body's Panel of Experts on Yemen echoes criticism by his opponents that Mr Saleh's rule from 1978 to 2012 was marred by corruption, and that even out of office he is fomenting instability - allegations he has consistently denied.

Presented with the experts' 54-page findings, the Council has voted unanimously to extend sanctions on Mr Saleh and two top militia leaders, first targeted by the world body in November for their alleged role in destabilising the country.

In an interview last year, Mr Saleh denied any corruption during his tenure.

His party has also rejected allegations by Mr Saleh's critics that he or his son Ahmad Ali, once one of Yemen's top military commanders, had had a hand in the fall of the capital Sanaa.

Most of this wealth was believed to have been transferred abroad under false names or the names of others holding the assets on his behalf, the report said. It took the form of property, cash, shares, gold and other valuable commodities, and was believed to spread across at least 20 countries.

Mr Saleh was ousted in the wake of the 2011 Arab Spring protests, after 33 years at the head of one of the Arab world's most fractious and - despite modest energy reserves - impoverished countries.

He has remained a power-broker, and frequently criticised his successor, Abd-Rabbu Mansour Hadi, in the months running up to the invasion of Sanaa in September by a Shi'ite Muslim rebel group that eventually swept Hadi from power and opened up a political vacuum.