WARSAW (Reuters) - Polish Prime Minister Donald Tusk criticised as "unacceptable" on Friday a Russian report on the plane crash that killed Poland's president, a view that may upset Warsaw's cautious rapprochement with Moscow.
President Lech Kaczynski, his wife Maria and 94 others, mostly senior Polish officials, died on April 10 when their Tu-154 plane crashed in thick fog near Smolensk airport in western Russia.
Russia, keen to mend long-strained ties with Poland, an increasingly important trade partner and influential member of the European Union, recently handed Poland its report on the causes of the crash after a months-long investigation.
Its content has not been made public and Tusk did not go into details of what it contained, but he said: "From the Polish point of view, the draft report from the Russian side as it has been sent is without question unacceptable."
The report does not comply fully with the Chicago Convention which regulates international air travel, he said in the televised comments to reporters in Brussels on the sidelines of a European Union summit.
"This negligence and mistakes or lack of positive reaction to what Poland has been asking for, all these things allow us to say that some of the report's conclusions are without foundation," Tusk said.
Russia is expected to study the Polish comments on the report and the two will then attempt to write a joint final version of what happened.
Moscow's first reaction to Tusk's criticism was cautious.
The Inter-state Aviation Committee, Russia's civil aviation authority which drew up the report, said it would not comment on politicians' remarks on the investigation, and Russia's Foreign Ministry said the issue should not be "politicised."
"It stands to reason that Russian experts will reply to the Polish side's questions," the Interfax news agency quoted Russian Foreign Ministry spokesman Alexei Sazonov as saying.
"The main thing is not to politicise the situation."
Poland's main representative on the investigation, Edmund Klich, has already expressed dissatisfaction with Russia's stance. For example, the two sides disagree about whether the flight should be classified as military or civilian -- a potentially crucial point in assigning responsibility for the decision to land in poor weather.
Kaczynski's identical twin brother Jaroslaw, who heads Poland's main opposition party, the right-wing Law and Justice (PiS), has accused Tusk and Moscow of effectively engineering the crash and of collaborating to cover up its real causes.
With parliamentary elections due next autumn, Tusk cannot afford to appear too soft in his dealings with Moscow, Poland's overlord in the Cold War era, even though most Poles support his government's drive to improve economic relations with Russia.
On a visit to Warsaw last week, Russian President Dmitry Medvedev signalled Moscow's interest in taking part in Polish privatisations, especially in the energy sector and also promised to cooperate with Poland over the plane crash probe.
(Additional reporting by Moscow bureau; Writing by Gareth Jones; Editing by Alison Williams)