"A leaked document in Qatar's embassy and a letter to Qatari Foreign Minister Mohammed bin Abdulrahman Al Thani on October 26, 2016, show Mohammed bin Salman and Mohammed bin Zayed's support for certain key al-Qaeda members in the Arabian Peninsula," Arabic language al-Badil newspaper wrote.

Based on the documents, US Treasury Undersecretary for Terrorism and Financial Intelligence said that the Saudi and Abu Dhabi crown princes have established continued contacts with two Yemeni nationals, namely Ali Abkar al-Hassan and Abdollah Faisal Ahdal, who are on the US blacklist of most wanted terrorists.

The documents also revealed the detailed activities and operations of the two Yemeni nationals in support of the al-Qaeda and the ISIL as well as Saudi Intelligence Chief Khalid bin Ali bin Abdullah al-Humaidan's financial support for them.

The documents were revealed after a new report released by a British think tank on Wednesday said that Saudi Arabia is the “foremost” foreign funder of Islamist extremism in the UK and other western countries.

The Henry Jackson Society — a right-wing think tank — said that overseas funding primarily from the governments and private charities of Persian Gulf countries has a “clear and growing link” to the onslaught of violence the UK and other western states.

The group estimated that the Saudi government and charities spent an estimated $4 billion exporting Saudi Arabia’s strict interpretation of Islam, known as Wahhabism (also practiced by ISIL and other terrorist groups), worldwide in 2015, up from $2 billion in 2007. In 2015, there were 110 mosques in the UK practicing Salafism and Wahhabism compared to 68 in 2007. The money is primarily funneled through mosques and Islamic schools in Britain, according to the report.

“Influence has also been exerted through the training of British Muslim religious leaders in Saudi Arabia, as well as the use of Saudi textbooks in a number of the UK’s independent Islamic schools,” the report said.

Although many Western countries, including the United States, have acknowledged the threat of foreign terrorist financing, Britain “has seen far less of a response from policy makers supporting moves to tackle the challenge of foreign-funded Islamist extremism,” the report said.