The remains of Polish Solidarity activist Anna Walentynowicz were swapped with the body of another victim, prosecutors said on Tuesday.

Investigators exhumed the two bodies last week after inconsistencies in documents provided by Russia, which oversaw the local investigation of the Smolensk disaster, raised doubts whether the correct remains were passed on to families.

The discovery will likely lead to further exhumations and spark further protests by some Poles over the investigation of the crash, which Russian authorities blamed on the crew of the government Tu-154 on April 10, 2010.

"The prosecutor's office is looking into the issue of exchanging the bodies and is investigating the evidence also from this angle," said Colonel Zbigniew Rzepa, a spokesman for the military prosecutor's office.

Disputes over the handling of the investigation have frayed the often testy relations between Moscow and Warsaw, whose investigators also blamed Russian traffic controllers for allowing the plane to attempt a landing in heavy fog.

The family of Anna Walentynowicz, whose sacking at the Gdansk shipyard in August 1980 sparked protests that led to the creation of the Solidarity trade union, said last week that they had proof that the body exhumed from a family grave in Gdansk was not hers.

"The question of finding grandma and making sure that her last will of resting next to her husband is fulfilled is one chapter which we are closing here," said her grandson, Piotr Walentynowicz.

"But we are now opening another chapter of who is responsible," he said.

The remains of the Smolensk victims, including then President Lech Kaczynski and his wife, were examined by Russian investigators in the presence of Polish officials in Moscow before being flown back to Warsaw in metal coffins.

Law and Justice, Poland's main opposition party led by Kaczynski's twin brother Jaroslaw, has criticised Prime Minister Donald Tusk and his government for its handling of the Smolensk investigation.

Some rightist groups have accused the Russian and Polish governments of being at least partially responsible for the disaster.

The prosecutors did not say whose remains were swapped with those of Walentynowicz.

Polish military prosecutors plan to exhume four additional bodies and representatives of families of other victims said they expected many more remains to be examined. (Reporting by Chris Borowski; Editing by Stephen Powell)

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