Traces of explosives have been discovered on the wreck of the Polish presidential jet which crashed in Russia in 2010, killing then president Lech Kaczynski and 95 other people, a newspaper reported Tuesday.
"Tests have confirmed the presence of TNT and nitroglycerine on 30 seats. The substances were also found on the area linking the fuselage with the wing," Poland's leading Rzeczpospolita daily said.
The recent tests were conducted by "Polish prosecutors and experts" it said, but testing by Polish and Russian investigator immediately after the 2010 crash had ruled out explosives.
Rzeczpospolita raised the possibility the reported explosives might be traced to unexploded World War II bombs in Smolensk, an area of western Russia which saw heavy fighting.
"We must wait for prosecutors to draw their conclusions and establish the source of the substance before taking any measures," government spokesman Pawel Gras told public TVP broadcaster.
Zbigniew Rzepa, spokesman for Polish military prosecutors supervising the investigation, refused to comment but said prosecutors were expected to issue a statement around noon.
A July 2011 Polish crash report blamed errors by the ill-trained crew for the crash.
The report admitted most of the blame for the April 2010 disaster -- in which all 96 people on board died -- lay with Poland, but also faulted Russia, where the plane went down in thick fog.
It had ruled out "extremist versions" of events, including sabotage and pressure from third parties on the crew to land despite bad weather.
The Russian investigation concluded that there was "psychological pressure" on the crew to land in dangerous weather conditions, prompting Warsaw to criticise their report as incomplete and riddled with errors.
Poland's conservative Law and Justice party -- led by Jaroslaw Kaczynski, the late president's twin brother -- has accused Prime Minister Donald Tusk's centre-right government of failing to take Russia to task.
A Law and Justice-run parliamentary commission that probed the crash blamed Russia, claiming it had forged the testimony of Smolensk's air traffic controllers, who it alleged had misled the pilots.
The doomed presidential delegation had been bound for a memorial ceremony in Katyn, near Smolensk, for thousands of Polish army officers slain by the Soviet secret police in 1940, a massacre denied by the Kremlin until 1990.