Prominent Islamabad-based Al Jazeera journalist Ahmed Muaffaq Zaidan was put on a watch-list of suspected terrorists by US authorities based on the suspicion that he was a member of Al Qaeda, The Intercept, reported on Friday.

The news portal — which reports on documents released by Edward Snowden and describes itself as a proponent of "fearless, adversarial journalism" — cited documents from 2012 provided by the National Security Agency (NSA) "whistleblower" Snowden.

The documents suggest that Al Jazeera's longtime Islamabad bureau chief, a Syrian national, was described in the NSA documents as "a member" of Al Qaeda and Muslim brotherhood.

In a phone interview, Zaidan told The Intercept that that he "absolutely" denied being a member of the terrorist organisation. He added that his career has had many years of dangerous work in Afghanistan and Pakistan which required him to conduct interviews with significant people in the region, which is a normal part of any journalist's career.

"For us to be able to inform the world, we have to be able to freely contact relevant figures in the public discourse, speak with people on the ground, and gather critical information. Any hint of government surveillance that hinders this process is a violation of press freedom and harms the public’s right to know," Zaidan told The Intercept. "To assert that myself, or any journalist, has any affiliation with any group on account of their contact book, phone call logs, or sources is an absurd distortion of the truth and a complete violation of the profession of journalism," he added.

The NSA and the office of the director of national intelligence declined to respond to questions pertaining to the basis of Zaidan's addition to the watch list and his alleged Al Qaeda affiliation.

The agency also declined to answer detailed questions about Skynet — a program that analyses communication data and location from call records in order to detect suspicious patterns — and how information about people it identifies is used.

CPJ concerned over US surveillance of Al Jazeera

The Committee to Protect Journalists (CPJ) has said it is "deeply troubled" by reports that the NSA spied on Zaidan.

"Colouring the legitimate news-gathering activities of a respected journalist as evidence of international terrorism risks chilling the vital work of the media, especially in Pakistan where journalists routinely interview Taliban and other militant groups as part of their coverage," CPJ's Asia programme coordinator, Bob Dietz, said in a statement.

"The NSA has once again brought the dangers of mass surveillance into sharp relief," CPJ Internet Advocacy Coordinator Geoffrey King from San Francisco, said. "Given a big enough pool of data, anyone can end up fitting a 'suspicious' pattern. Journalists who traverse many sectors of society to bring the public the news are particularly vulnerable."

Zaidan and Al Jazeera strongly defended the journalist's reporting and rejected the US's suspicions, The Intercept reported.