By Chris Borowski

WARSAW (Reuters) - One of Poland's best-selling newspapers fired its most senior editors on Tuesday over a "flawed" article that triggered a political row when it said traces of explosives had been found in the wreckage of a presidential jet that crashed in 2010.

Polish prosecutors denied a report last week by the Rzeczpospolita daily which alleged they had found traces of TNT and nitro-glycerin on the wings and in the cabin of the jet, which killed Polish President Lech Kaczynski and 95 others when it crashed in Russia two years ago.

The report, which cited unnamed sources, prompted the late-president's twin brother and opposition leader Jaroslaw Kaczynski to lash out at Prime Minister Donald Tusk over his handling of the affair, which he called a "heinous crime".

In a statement in Rzeczpospolita's Tuesday edition, its supervisory board said it had recommended that Editor-in-Chief Tomasz Wroblewski, his top deputy, and the two leaders of the national section be dismissed.

"The reporters associated with the publication did not have the grounds to state that traces of TNT and nitro-glycerin were found in the wreckage," the newspaper said. "We deem the text to be flawed and inadequately documented."

The board also asked for the author of the article to be fired after he failed to provide any written proof to back up his sources.

Grzegorz Hajderowicz, Rzeczpospolita's owner and the head of its supervisory board, confirmed the sackings had taken place.

"Consequences have to be paid for wrong decisions, hence the dismissals and disciplinary firings," he said in a separate statement on the paper's website.

Rightist groups led by Kaczynski's Law and Justice party have accused investigators of failing to unearth the real reason for the crash with many suggesting that Warsaw and Moscow have colluded in a cover-up.

Official reports say the jet crashed into the ground after losing one of its wings when it clipped a birch tree on its approach to a small airport in Smolensk, western Russia.

Russian investigators blamed the Polish crew for trying to land in heavy fog and misjudging their altitude, while their Polish counterparts said the Russian airport controllers should not have allowed the plane to attempt such an approach.

Polish military prosecutors said evidence of high energy particles had been found in the wreckage, but cautioned such material often yielded false positives, saying the samples would require further testing to determine whether there were traces of explosives too.

Prosecutors have admitted that at least four victims in the plane crash were misidentified and given to the wrong families to be buried, fuelling conspiracy theories.

(Editing by Andrew Osborn)