BERLIN, Feb 17 (Reuters) - A former German spy chief who was sacked after being accused of averting his eyes to the threat posed by the far-right founded a new right-wing party on Saturday, holding an inaugural party congress on a boat near Germany's old capital Bonn.

The party is the third to be founded this year in Germany, further fragmenting the political landscape and making electoral predictions tricky ahead of European parliamentary polls and votes in half the country's municipalities and three states.

The Werteunion, or Values Union, is headed by Hans-Georg Maassen, who was dismissed as head of Germany's Office for the Protection of the Constitution (BfV) in 2018.

Maassen was forced to resign after initially questioning the authenticity of a video showing far-right extremists chasing migrants in the eastern city of Chemnitz, saying it might have been faked.

He later toned this down, saying the interpretation of the video was open to question, not its authenticity, but this was not enough to quell the outcry that led to his departure.

The lawyer has since become known for his increasingly radical commentary on immigration, becoming a hero to far-right activists including some in the circles surrounding Heinrich XIII Prince Reuss, the aristocrat who led a foiled coup in 2022.

A former member of the opposition Christian Democrats, Maassen is himself now being monitored by the security agency he ran, he said last month. The BfV said privacy law meant it could not comment on individual cases.

"12:32 o'clock. Done!" Maassen said on social media platform X, posting a photo of himself and colleagues in front of a German flag on the boat.

With Germany's mainstream parties well down in polls compared to their 1980s heyday when the Christian Democrats and the Social Democrats regularly polled near 50%, many new parties have sought to capitalize on frustration with the establishment.

Earlier this year, leftist politician Sahra Wagenknecht founded a new left populist party.

The Werteunion, once a pressure group aligned with the Christian Democrats, will now jostle for space with the far-right Alternative for Germany (AfD), which tops polls in some eastern states.

While all other parties have ruled out working with the AfD, Maassen recently said he would be prepared to back their legislative proposals if they made sense - though he ruled out a coalition with the party.