The black box salvaged from the devastating plane crash that killed Poland's president and scores of political and military leaders showed that flying error was the most likely cause of the accident, with no sign that the pilot was put under pressure to land, Russian investigators said yesterday.

The Russian-built Tupolev 154 plane, carrying Lech Kaczynski and his entourage, hit trees and burst into flames last Saturday as it was attempting to land in thick fog at Smolensk airport in western Russia. All 96 people on board were killed.

Before the crash the pilot made attempts to land at the airport, which was not equipped with modern guidance systems normally used in bad visibility.

There had been intense speculation that the president put pressure on the pilot to land despite warnings that conditions were dangerous, because diverting would have led to his party missing an anniversary event of major political significance to Poland.

But Russian investigators, who have been examining two of the three flight recorders retrieved from the wreckage, said yesterday there was no evidence the pilots had been subjected to pressure.

"There is no confirmation that any of the high-ranking passengers ordered the pilots to land at Smolensk," said a spokesman.

Investigators said the most likely cause of the crash appeared to be pilot error. However the Russian investigators' report was not final. A third black box is being examined by Warsaw investigators.

During the Russian invasion of Georgia in 2007, Mr Kaczynski tried to persuade a pilot to land at Tbilisi airport.

The pilot refused because of the risk of the aircraft being hit by gunfire and the flight was diverted. The president later entered Georgia by car.