American and European security agencies are reportedly investigating a possible new whistleblower behind the WikiLeaks publication that exposed alleged NSA spying on top French officials, including three presidents.

The website on Tuesday released what appear to be classified NSA documents alleging the US agency spied on three successive French presidents: Jacques Chirac, Nicolas Sarkozy and incumbent François Hollande.

READ MORE: ‘Espionnage Élysée’: WikiLeaks claims NSA spied on Hollande, Sarkozy and Chirac

Responding to the report, Hollande called such activities unacceptable, while the French justice minister said WikiLeaks founder Julian Assange and NSA whistleblower Edward Snowden could be offered symbolic asylum in the country. US President Barack Obama assured his French counterpart the US hadn’t spied on him.

While Snowden, who leaked thousands of classified NSA files to world media outlets in what he described a justified exposure of illegal activities of the American government, the new documents may not have originated from him, Reuters reported on Saturday, citing security sources familiar with the matter.

An investigation into a possible new whistleblower working with WikiLeaks is underway in the US and Europe, the news agency said. No concrete proof of such a figure’s existence have yet been uncovered yet, it added.

Earlier, media reports based on Snowden’s documents alleged the NSA surveillance teams targeted the personal communications of German Chancellor Angela Merkel. German prosecutors investigated the allegations, but failed to obtain any court-admissible evidence to make a case.

Snowden is living in Russia, which granted him political asylum after he was stranded in a Moscow airport due to the US cancelling his passport, as he was en route to Latin America. Assange is currently being harbored by the Ecuadoran embassy in London, where he is shielded from extradition.