New evidence has come to light of a possible link between Saudi Arabian officials and the 9/11 terrorist attacks, further raising tensions as President Obama travels to the kingdom.

Ghassan Al-Sharbi, a Saudi who became an al-Qa’ida bomb maker, is believed to have taken flying lessons with some of the 9/11 hijackers in Arizona but did not take part in the attacks on New York and the Pentagon that killed 3,000 people in 2001.

He was captured in Pakistan in 2002 and has since been held at Guantanamo Bay. According to a US memo — known as document 17 — written in 2003 and quietly declassified last year, the FBI learnt that he had buried a cache of papers shortly before he was captured.

Document 17 was written by two US investigators examining the possible roles of foreign governments in the attacks. One detail leapt out at them from the papers that Sharbi had tried to hide: his US flight certificate was in an envelope from the Saudi embassy in Washington.

Brian McGlinchey, the activist who uncovered document 17, said: “The envelope points to the fundamental question hanging over us today: to what extent was the 9/11 plot facilitated by individuals at the highest levels of the Saudi government?”

President Obama is expected to meet on Wednesday with King Salman, whose kingdom is under pressure from low oil prices, an emboldened Iran and Washington’s tougher stance. The Saudi government threatened last week to dump $750 billion in US Treasury securities and other American assets if congress passes a bill that would clear a path for the families of 9/11 victims to file lawsuits against the kingdom. Hillary Clinton and Bernie Sanders, the Democratic presidential candidates, backed the bill, which Mr Obama has signalled he will veto.

Donald Trump and Ted Cruz, the leading Republicans in the race, have warned Saudi Arabia that its relationship with the US must change. “Friends do not fund jihadists that are seeking to murder us,” Mr Cruz said.

Mr Obama also faces calls to release a redacted 28-page portion of a joint congressional report on the 9/11 attacks, produced in 2002 and thought to link senior Saudi figures to the plot. He suggested on Monday that a decision was imminent.

The pages are in a secure room beneath the US Capitol. Congressmen can read them, but are watched to make sure they do not make notes. Thomas Massie, a Republican from Kentucky, said: “I had to stop every couple of pages ... to rearrange my understanding of history.”

Bob Graham, a former chairman of the US senate intelligence committee, has alleged that Saudi Arabia was the principal financier of 9/11. “The effect of withholding [the pages] has been to embolden Saudi Arabia to be a continuing source of financial and human terror resources,” he said.

Document 17, written by Dana Lesemann and Michael Jacobson, will deepen suspicions. Ms Lesemann is said to have been sacked from the 9/11 commission after she circumvented her boss to access the 28 pages.

Mr Jacobson was the principal author of the 28 pages, and document 17 hints at his suspicions. “How aggressively has the US government investigated possible ties between the Saudi government and/or royal family and the September 11th attacks?” it asks.

The Times