Poland's Prime Minster Donald Tusk says he is going to look into reports that traces of explosives were found on the wreckage of the plane in which Poland's President Lech Kaczynski was killed in 2010.
Ninety-five other people on the flight also died when the plane crashed near Smolensk-Severny airport.
One of Poland's biggest newspapers, Rzeczpospolita, said traces of TNT and nitroglycerin were found on the plane's wings, inside the cabin and the area surrounding the crash site.
The report has revived speculation the president was assassinated, although it has been pointed out the traces might be from World War II bombs which can still be found in the Katyn Forest area, where Soviet security police shot more than 22,000 Poles in 1940.
Investigators are also considering the possibility the traces of explosives found could have come from the soil at the crash site, which once served as a military test range.
A government report in 2011 said the crash was not caused by an explosion but the Polish authorities did not have full access to the wreckage at that time.
The latest development comes shortly after a key witness in the inquiry was found hanged in the basement of his house in the outskirts of Warsaw. A post mortem is due to be held this week.
Remigiusz Mus, 42, was apparently due to tell investigators he heard two loud bangs just before the president's plane went down.
The former flight engineer also claimed he overheard a conversation between a Russian air traffic control officer and Mr Kaczynski's pilots while he was in the cabin of another aircraft which had just landed with a number of Polish journalists on board.
According to Mr Mus, the air traffic controller allowed it to descend in spite of heavy fog that severely restricted visibility on the day.
The head of the Polish Parliamentary Investigation Commission, Antoni Macierewicz, has called for the second main witness, a pilot on the journalists' plane, to be placed under protection from now on.
"We have an impression that the noose is tightening around the necks of anyone who knows what really happened in Smolensk," he said.