A Polish report on the 2010 plane crash in Russia that killed President Lech Kaczynski and 95 others says Russian air traffic controllers gave incorrect and confusing landing instructions to pilots, a finding that could test already strained ties between the neighbours.

It challenges a Russian aviation commission report published in January that put sole blame for the disaster on Polish officials — and struck Poles as an attempt to avoid any responsibility for the plane crash in heavy fog at a rudimentary airport near Smolensk.

Since then, Poles have eagerly awaited their own experts’ report, hoping it would create a more balanced picture of the crash. The accident on April 10, 2010, killed dozens of senior officials along with the president and first lady, in the worst Polish disaster since World War II.

The Polish report presented on Friday does not shy away from putting most of the blame on Polish officials and procedures.

As key causes of the crash it cites wrong positioning of the plane during attempted landing, due to insufficient training of the pilots to fly the plane, a Tupolev-154. It also cites a lack of proper cooperation among the crew and an overly slow reaction to an automatic terrain warning system that warned pilots they were flying too low. Incorrect information from the airport control tower on the plane’s position prevented the crew from realizing they were making mistakes, it said.

“There was no single cause, but an accumulation of causes led to the crash,” said Jerzy Miller, the interior minister and head of the investigation commission, at a three-hour presentation of the findings.

In Moscow, deputy chairman of Russia’s State Duma’s foreign affairs committee, Andrei Klimov, told the Associated Press he believes the Polish pilots are to blame and lashed out at Warsaw for what he called politicizing the investigation.

“This report is not a technical, but a political one,” Mr. Klimov said. “The results were compiled with a nod to the political situation in order to show that Russians were to blame for at least something.”

The report says that the main pilot, Capt. Arkadiusz Protasiuk, 36, did not have sufficient experience in flying a Tu-154 or in landing under difficult conditions. The only crew member who spoke Russian and could communicate with the airport, Protasiuk was overwhelmed by many tasks and by the difficult conditions, the report said.

It insisted Russian air traffic controllers played a role in the tragedy, too. Polish investigators found that the Polish plane was flying about 200 feet lower than the pilots believed in the moments before the plane clipped a tree and crashed. The Polish commission said the Russian air traffic controllers confirmed the plane was on the right course for descent, information that made the crew continue in the false belief they were on making a proper approach.

The Polish report, which is available on the Internet in Polish, Russian and English, said the Russian air strip had insufficient lighting, contributing to a lack of visibility that morning.

Russian investigators said in January that the Polish pilots faced undue pressure from political officials to try to land the plane in heavy fog and with no visibility — a hugely sensitive issue. They said the then-head of the Polish air force, Gen. Andrzej Blasik, who had some alcohol in his blood, entered the cockpit and pressured the pilots to risk a dangerous landing.

The Polish report differs on that point, too. It confirms Gen. Blasik’s presence in the cockpit, but says it did not play a role in the crash.

Polish experts said they did not find any pressure on the crew and that pilots were not actually making a landing when the plane clipped a tree and crashed, just hundreds of meters from the runway. They had attempted an approach but were just starting to abort it, unable to see the ground and amid commands from a warning system to pull up.

“The crew were making the right decisions, but they did not know how to carry them out properly” due to insufficient training, Mr. Miller said.

The Polish plane crashed when Lech Kaczynski and his delegation were on their way to honour some 22,000 Polish officers killed during World War II by Stalin’s secret police, a crime known as the Katyn massacres.

The symbolism of the plane disaster occurring on a mission to remember added another layer of Polish national grief and resentment in the weeks and months after the crash.

At first it seemed the accident had helped Poland and Russia heal some of their historic wounds, because an outpouring of sympathy by Russians was met by Poles with much gratitude.

But the Russian report again strained relations, adding to a lingering sense of aggrievement in Poland. Poles remain bitter about the Katyn massacres, the Soviet Union’s occupation of Poland’s eastern half during the war and Moscow’s domination of Poland during the Cold War.

Right-wing groups have promoted conspiracy theories, with some saying they believe Russians killed Kaczynski and the others by producing artificial fog that blinded the pilots.

Mr. Miller said there was no artificial fog at the Smolensk airport that day.

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