Kiev (AFP) - Ukraine's most prominent political talk show host was stripped of his work permit on Tuesday in what he described as a politically-charged case.

The incident created an instant political uproar in Kiev that eventually forced Ukrainian President Petro Poroshenko to step in and defend his record on media rights.

Savik Shuster -- a 63-year-old Canadian citizen who was born in the Soviet Union and had previously worked for the US-funded Radio Liberty station -- accused Kiev's pro-Western leaders of being thin-skinned and unwilling to support free speech.

"The problem is that, as it turn out, this government does not tolerate any criticism," he said on his 3S.tv satellite television channel.

He later announced he was going on hunger strike "until the moment when my right to work in Ukraine is restored".

The Organisation for Security and Cooperation in Europe's press freedom representative Dunja Mijatovic said the case raised "a number of concerns and questions" about Ukraine.

Shuster was told by the employment office Tuesday that his Ukrainian work permit was being revoked because he had failed to notify registration authorities that he was the subject of a disputed tax evasion claim.

He has produced his political talk show, now called "Shuster Live", for a number of years on various Ukrainian channels prior to launching his own channel.

Shuster, one of Ukraine's most recognised television personalities, promised to continue his work despite lack of permit.

Prior to moving to Ukraine, Shuster had developed a reputation in Russia for providing a venue for voices critical of the government.

The Kremlin's seizure of most media assets under President Vladimir Putin saw him blacklisted in Russia and forced to relocate to Kiev in 2005 -- the year Ukraine enjoyed its first pro-Western government.

But the most recent EU-backed leadership in Ukraine -- now riven by a pro-Moscow insurgency in the east -- has been criticised heavily for banning Russian movies and television programmes on political grounds.

Ukraine ranked 107th out of 180 countries on this year's Press Freedom Index prepared by the Reporters Without Borders (RSF) media advocacy group, up from 129 the year before.

Shuster's case created immediate controversy that saw Poroshenko step in and reaffirm his commitment to basic rights.

"Freedom of speech is one of Ukraine's greatest achievements," he wrote on Facebook.

"As the guarantor of the constitution, I have and will protect free speech in all its forms. That is why I hope that the corresponding (government) agencies resolve this matter as soon as possible."