KRAKOW, Poland (Reuters) - Polish prosecutors on Monday began the exhumation of President Lech Kaczynski, who died in a plane crash in Russia in 2010, to examine his remains as part of an investigation into the tragedy likely to deepen political divisions in Poland.

A man prays in front of the sarcophagus of the late President Lech Kaczynski during an event commemorating the first year anniversary of his funeral in Krakow April 18, 2011. REUTERS/Kacper Pempel

The crash near Smolensk in western Russia, which killed 96 people including Kaczynski’s wife, top army brass and the central bank governor, has become one of the most fraught public issues in Poland, with some claiming foul play.

An inquiry by Poland’s previous, centrist government ruled pilot error caused the government’s Soviet-made TU-154 to crash into the ground in heavy fog during an attempt to land.

But Kaczynski’s twin brother Jaroslaw, whose nationalist-minded Law and Justice party (PiS) unseated the centrists in an election last year, has said an onboard explosion could have caused the crash.

Prosecutors want to determine whether there was no mix-up of remains during burial, as well as whether damage to the bodies had been described correctly in previous inquiries, arguing that Russia’s refusal to return the plane’s wreckage was a critical obstacle.

“The crucial evidence remains in Russia and I don’t expect to have access to it any time soon,” Marek Pasionek, a deputy prosecutor general, was quoted saying by Rzeczpospolita daily last week.

“We need to have the wreckage in order to reconstruct the flight. “And however brutal this may sound, the bodies are practically the only piece of evidence which we can have access to, through exhumations.”

Russia has said the wreckage cannot be returned until its own criminal inquiry is concluded.

PAINFUL DEBATE

The remains of Kaczynski and his wife Maria will be removed from their crypt in the Wawel cathedral in Krakow in southern Poland after it closed for tourists at 6 p.m. local time (12 p.m ET). Other exhumations will follow in coming months.

Critics say the new investigation amounts to a politically-motivated effort to discredit the centrist opposition and rally a conservative electorate deeply distrustful of Russia.

Kaczynski has long accused Donald Tusk, who was the prime minister in 2010 and now heads the European Council of heads of EU states, of being indirectly responsible for the crash - caused, in his view, at least partially by government negligence.

“The Smolensk crash continues to fan heated public tensions,” said Izabella Sariusz-Skąpska, daughter of a Polish activist who died in the crash.

“We don’t know how long (the investigation) will last ... Maybe the calculation is to have fireworks ready for the next election campaign,” she told Reuters.

Sariusz-Skapska’s father was flying with Kaczynski and his entourage to a ceremony to mark the 70th anniversary of the Katyn massacre, when Soviet secret police killed thousands of Polish officers in a forest in western Russia. Her father headed an association of the Katyn victims’ families.