People in Poland are lining up to pay their respects to president Lech Kaczynski and his wife, who are lying in state in closed coffins in the capital's presidential palace.

Maria Kaczynska's body was returned home on Tuesday morning to be placed next to her husband, following a fatal plane crash on Saturday that killed all 96 people aboard.

Jonah Hull, Al Jazeera's correspondent in Poland, said the palace in Warsaw had "become a shrine", with people laying flowers and photos at the feet of the caskets.

"The presidential palace has become a focal point for that public grief, a shrine it has become with an ever-growing sea of candles brought and lit by people as a sign of respect and remembrance.

"Hundreds of people are still here, it is a normal working day but that hasn't stopped people coming," he said.

Special observance

Parliament has held a special observance in memory of Kaczynski and the politicians killed in the disaster.

The bodies of the first couple are to lie in state in the Columned Hall of the Presidential Palace, where the president appointed and dismissed governments.

The couple are expected to be buried in Wawel castle in the southern city of Krakow on Sunday, Poland's PAP news agency said.

Kaczynski and his entourage had been travelling to mark the 70th anniversary of the massacre of Polish officers by Soviet secret police near Smolensk when his plane went down in thick fog.

So far, 87 bodies have been recovered and 40 of them identified, Andrzej Seremet, Poland's chief prosecutor said.

The body of the president's wife arrived at Warsaw's Okecie airport shortly after 10:30 local time on Tuesday.

It was greeted by her only child, daughter Marta, who knelt by the casket and wept, and Jaroslaw Kaczynski, the twin brother of the late president.

Election date

Earlier on Tuesday Poland's acting president said he will announce the date of the country's presidential elections on Wednesday to end uncertainty over the country's leadership.

"The election date must be set. This must be done as soon as possible to shorten the period in which Poland is in a period of uncertainty," Bronislaw Komorowski told TVP Info television.

According to the Polish constitution, the election must take place within 60 days, or two months, of the announcement.

The country had been due to hold a presidential election in October, when Kaczynski, a conservative, was expected to run against Komorowski, a liberal.

Poland has moved to fill important positions in the state administration, after dozens of political and military leaders were among the 96 killed in Saturday's crash.

'Human error'

Russian investigators have suggested human error may have been to blame for the crash, saying that there were no technical problems with the Soviet-made plane.

Alexander Bastrykin, Russia's chief investigator, said on Monday the flight recorders revealed that while there were "no problems with the plane", the pilot decided to land despite warnings about bad weather conditions.

Polish media have speculated that the pilots were pressured by people aboard the jet to land quickly so as not to miss the memorial ceremony.

But Andrzej Seremet, Poland's chief prosecutor, said there was no evidence to support the claim.

Investigators in Poland are expected to listen to cockpit conversations from the flight recorders, also known as "black boxes", to see if there were "any suggestions made to the pilots" from other people aboard the aircraft.