He has been gone from the capital for eight years, but Prince Bandar bin Sultan, who as Saudi Arabia’s ambassador to Washington wielded influence over no fewer than five different US presidents, has re-emerged as a pivotal figure in the struggle by America and its allies to tilt the battlefield balance against the regime in Syria.

Appointed by the Saudi king, his uncle, last year as the head of the Saudi General Intelligence Agency, Prince Bandar has reportedly for months been focused exclusively on garnering international support, including arms and training, for Syrian rebel factions in pursuit of the eventual toppling of President Bashar al-Assad.

It is a long-term Saudi goal, that in the past several days has been subsumed by the more immediate crisis over the purported use of chemical weapons by Damascus, which, according to Riyadh, must be met by a stern response. That message is being delivered to President Barack Obama by the current Saudi Ambassador in Washington, Adel al-Jubeir, who is a Bandar protégé.

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It was Prince Bandar’s intelligence agency that first alerted Western allies to the alleged use of sarin gas by the Syrian regime in February.

While a trip earlier this month to the Kremlin to try to cajole President Vladimir Putin into withdrawing his support for President Assad reportedly failed, Prince Bandar automatically has greater leverage in Western capitals, not least because of friendships forged during his time in Washington. His most recent travels, rarely advertised, have taken him to both London and Paris for discussions with senior officials.

As ambassador, Prince Bandar left an imprint that still has not quite faded. His voice was one of the loudest urging the United States to invade Iraq in 2003. In the 1980s, Prince Bandar became mired in the Iran-Contra scandal in Nicaragua.

Months of applying pressure on the White House and Congress over Syria have slowly born fruit. The CIA is believed to have been working with Prince Bandar directly since last year in training rebels at base in Jordan close to the Syrian border.

The Saudis are “indispensable partners on Syria” and have considerable influence on American thinking, a senior US official told The Wall Street Journal yesterday. He added: “No one wants to do anything alone”.