polandWARSAW (AFP) - – Fresh protests erupted in Poland Wednesday over a decision to bury president Lech Kaczynski in a castle with Polish kings that has ruptured the national unity since his death in a plane crash.

The funeral of Kaczynski and his wife takes place Sunday in the cathedral of Krakow's Wawel castle. US President Barack Obama, Russian leader Dmitry Medvedev and Britain's Prince Charles are among foreign dignitaries attending.

But hundreds of people took to the streets for a second day and more than 38,000 joined a Facebook campaign against the couple's burial in a spot where Polish royalty and historical figures are laid to rest.

"I've come here because the Wawel is a necropolis for Polish kings, for people of the stature of poets like Mickiewicz or Slowacki," two iconic 19th century bards," said Aleksandra Kozlowski, a protester in Warsaw.

Around 200 people rallied in central Warsaw and hundreds of demonstrators also turned out in the Baltic port of Gdansk, Poznan in the west, and in Krakow itself.

The rallies were in stark contrast to the thousands of mourners paying their respects to the Kaczynskis at the presidential palace following the air disaster in Russia on Saturday which killed them and 94 others.

The powerfully symbolic location for the burial was chosen by Kaczynski's family, officials said.

But the nationalist and deeply Catholic Kaczynski, in office since 2005, was a highly divisive figure at home and abroad. His identical twin Jaroslaw is leader of Poland's conservative opposition and a former prime minister.

"This decision will spark protests and could cause the deepest splits in Polish society since 1989," Oscar-winning film-maker Andrzej Wajda wrote in an open letter published on the website of the liberal daily Gazeta Wyborcza.

Parliamentary officials said earlier Wednesday that snap elections to replace Kaczynski would be held on June 13 or 20. Interim president Bronislaw Komorowski said after meeting members of parliament that the final date would not be announced until April 21.

Under the Polish constitution Komorowski, who is also the parliament speaker, must call the election within two weeks of the president's death and the ballot must be held within 60 days of the announcement, meaning the ballot would fall on June 20.

Komorowski, a liberal, had been expected to run against Kaczynski in the October election. The deceased president's twin brother, Jaroslaw, who was premier in 2006 and 2007, may take his sibling's place but has made no public statement.

The remains of Lech Kaczynski, 60, and his wife Maria, 66, have been lying in state at the presidential palace in Warsaw since Tuesday, drawing tens of thousands of mourners of all ages.

Queues stretched for more than a kilometre (around half a mile) and families waited in the cold for up to 10 hours before filing silently past the closed coffins. Related article: Poles flock from afar to mourn presidential couple

A plane carrying the bodies of 30 more victims arrived home from Moscow on Wednesday. Prime Minister Donald Tusk attended a ceremony for them while their coffins have been laid in a sports arena so relatives can pay their respects.

Poland extended the mourning period by one day until Sunday for the victims of the crash, many of them top military and political figures, which happened as the jet taking them to a memorial for a World War II massacre at Katyn near Smolensk tried to land. Related article: World leaders to attend funeral

The tragedy has brought signs of rapprochement between Moscow and Warsaw after years of bad blood, especially over the Katyn massacre, in which Soviet secret police slaughtered thousands of top Polish officers 70 years ago.

Russian investigators have pointed to pilot error. Air traffic controllers say the crew refused three times to heed advice to divert to another airport because of fog.

Investigators have ruled out a fire or explosion as the cause.