Former Saudi foreign minister Prince Saud al-Faisal has died, two months after he retired following 40 years in the job.

A statement from the Royal Court on Thursday said Prince Saud, who was born in 1940, died in the United States. No cause was given for his death, but he had faced many health problems.

Prince Saud, who was appointed in 1975, was the world's longest serving foreign minister when he was replaced on April 29 by Adel al-Jubeir, the then ambassador to Washington.

His tenure saw Israel invade Lebanon in 1978, 1982 and 2006, the eruption of Palestinian intifadas in 1987 and 2000, Iraq's invasions of Iran in 1980 and Kuwait in 1990, and the occupation of Iraq by a US-led coalition in 2003.

Prince Saud served under four Saudi kings, advancing the kingdom's foreign policy, especially after the attacks of September 11, 2001 in the United States.

He was also part of Saudi Arabia's efforts to lessen Iran's influence in the region, including the continuing conflict in Syria, where Saudi Arabia has been supporting several rebel groups.

Asked in early 2012 if it would be a good idea to arm Syria's rebels, he said briskly: "I think it's an excellent idea."

'Well liked and respected'

Prince Saud, a son of King Faisal, was born in Taif near Mecca, where in 1989 he helped negotiate the agreement that ended Lebanon's 15-year civil war.

A degree at Princeton in the 1960s was followed by years at the Petroleum Ministry, where he was taken under the wing of his father's canny and charismatic oil minister Ahmed Zaki Yamani.

His career as a diplomat began traumatically: the new King Khaled named him as foreign minister following the assassination of Prince Saud's father Faisal, who had retained the foreign affairs portfolio after being made king in 1962.

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As the foreign minister of an important political and economic US ally in the region, Prince Saud was reported to have been well liked and respected in diplomatic circles.

Barack Obama, the US president, expressed his condolences to the deceased's family and described him as "a committed and accomplished diplomat". The US embassy in Saudi Arabia quoted Secretary of State John Kerry on Twitter as saying that "Saud was not only the longest-serving foreign minister, but was also one of the wisest".

جون كيري: لم يكن الأمير سعود أقدم وزير خارجية فحسب ولكنه كان من بين الأكثر حكمة أيضا #وفاة_الأمير_سعود_الفيصل pic.twitter.com/OYPi1PrgEd — U.S. Embassy Riyadh (@USEmbassyRiyadh) July 9, 2015

He was often described as a charismatic leader, willing to talk to reporters, and with a sense of humour.

With age, Prince Saud faced many health problems. In the last few years, despite suffering from chronic back pain and having various surgeries, he maintained his challenging role.

Witness of history

When he was appointed in October 1975, the region was dominated by Cold War rivalries, and secular pan-Arab nationalism seemed to be the future.

Egypt and Israel had not yet made peace, and Yasser Arafat led the Palestine Liberation Organisation from refugee camps in Lebanon. The shah still ruled Iran, while in Iraq a young Saddam Hussein was plotting his path to power.

Riyadh's relationship with Saddam, which went from wary support during the Iran-Iraq war to fierce enmity after the invasion of Kuwait, dominated foreign policy for long periods during Prince Saud's tenure.

Obituary: Prince Saud al-Faisal

But despite that complicated history, Prince Saud publicly argued against the 2003 invasion, presciently warning of a chaotic aftermath that could destabilise the region.

"If change of regime comes with the destruction of Iraq, then you are solving one problem and creating five more problems," he said in a British television interview.

In 2002, he launched King Abdullah's biggest foreign policy initiative, an Arab plan for peace with Israel in return for a withdrawal from all occupied land and a resolution of the refugee problem.

"All the neighbourhood, if you will, will be at peace with Israel, will recognise their right to exist. If this doesn't provide security of Israel, I assure you the muzzle of a gun is not going to provide that security," he said at the time.

Israel never agreed to the plan and Prince Saud said frequently that the failure to help create a Palestinian state was the biggest disappointment of his career.