A volcanic ash cloud that has shut down Europe’s airports threatened on Friday to disrupt a state funeral for Polish President Lech Kaczynski due to be attended by world leaders including U.S. President Barack Obama.

Kaczynski’s family wants Sunday’s funeral in Krakow to go ahead as planned, a presidential aide said. Senior officials were expected to take a final decision later in the day.

Tens of thousands of mourners continued to file past the coffins of Kaczynski and his wife Maria in Warsaw’s presidential palace. Some had been waiting up to 18 hours to view the coffins, a measure of the grief felt by many Poles over the worst single disaster to hit their country since World War Two.

The heads of Poland’s armed forces, its central bank governor and opposition lawmakers were also among the 96 people killed last Saturday when their ageing Tupolev plane crashed in thick fog while trying to land near Smolensk in western Russia.

As well as Obama, Russian President Dmitry Medvedev, German Chancellor Angela Merkel, French President Nicolas Sarkoy, Britain’s Prince Charles and dozens of other heads of state and government and royalty are all scheduled to attend the funeral.

Krakow’s Balice airport, which would handle most arrivals, shut down on Friday along with most other Polish airports because of the volcanic ash cloud spreading from Iceland.

“I wish to say that the (Kaczynski) family’s will is that the date of the funeral should not be postponed under any circumstances,” presidential aide Jacek Sasin told reporters.

Earlier, he said delaying the funeral would be a “last resort”.

The volcano in distant Iceland has been spewing ash into the atmosphere since Wednesday, causing air traffic disruption on a scale not seen since the Sept. 11 attacks in 2001 and leaving hundreds of thousands of travellers stranded across Europe.

Volcanic ash contains tiny particles of glass and pulverised rock that can damage engines and airframes. Experts say the ash could cause problems to air traffic for up to six months if the eruption continues.

CONTROVERSIAL PRESIDENT

Polish authorities had intended to fly the coffins to Krakow for the funeral at the city’s Wawel cathedral after a planned memorial service in Warsaw on Saturday.

The decision to bury the Kaczynskis at Wawel, usually reserved for Poland’s kings and national heroes, was already controversial. Some Poles believe Kaczynski does not deserve such an honour and have staged noisy protests against the move.

Public support for Kaczynski, a polarising nationalist and eurosceptic, had dwindled to just 20 percent before his death. Polls showed he would have lost to Bronislaw Komorowski, the candidate of Prime Minister Donald Tusk’s centrist Civic Platform (PO), in a forthcoming presidential vote.

Komorowski, who is also speaker of parliament, became acting president after Kaczynski’s death. It is unclear who will now be his main rivals in an election likely to take place on June 20.

Kaczynski was the candidate of his twin brother Jaroslaw’s right-wing Law and Justice (PiS). The candidate of the main leftist opposition party SLD also died in the crash.

Kaczynski and his entourage had been travelling to mark the 70th anniversary of the massacre of some 22,000 Polish officers by Soviet forces in Katyn forest when their plane crashed.

The exact cause of the crash remains unclear, though Russian officials say the pilot ignored advice from air traffic controllers to divert to another airport because of the fog.

Some Polish media have speculated that Kaczynski, in his determination not to miss the Katyn event, may have ordered the pilot to try to land the plane against the Russians’ advice.

On Thursday, Polish prosecutors promised to release details of the plane’s cockpit voice recorders which are being analysed.

Russia’s state-run RIA Novosti news agency, citing the Interstate Aviation Committee, said on Friday preliminary findings of the investigation showed the plane touched treetops one kilometre before reaching the landing strip.

(Additional reporting by Chris Borowski, Pawel Florkiewicz in Warsaw, Amie Ferris-Rotman in Moscow)