Prince Turki al-Faisal is currently ambassador to the UK and Ireland

The foreign ministry in Riyadh said Prince Turki al-Faisal would take up the diplomatic post in Washington.

A ministry statement said Prince Bandar had asked King Fahd to "relieve him of his duties for private reasons".

It praised his "exceptional gifts" during some 20 years of "distinguished service" as ambassador to the US.

Rumours that Prince Bandar had submitted his resignation surfaced at the end of last month, and were initially played down by the embassy in Washington.

PRINCE TURKI AL-FAISAL Saudi ambassador to London from 2003 to present Head of Saudi foreign intelligence 1977 to 2001 Brother to Saudi Foreign Minister Prince Saud al-Faisal Born in 1945 in Mecca, educated in US and UK Profile: Prince Turki al-Faisal

But he is known to be in poor health and is thought to want a senior job back home, such as head of intelligence, which is currently vacant.

Prince Bandar has played a critical role in building the special relationship between Riyadh and Washington, and has had extraordinary access to US presidents for three decades.

He leaves at a time when that relationship is under great pressure, particularly following the 11 September 2001 attacks and the subsequent war on terror.

The process of nominating Prince Turki to the role is now under way, the ministry statement said.

Prince Turki has been the ambassador in London since early in 2003.