The Russian Prosecutor General's investigations committee has opened an investigation into the crash.

"The investigation is looking into various theories...including unfavorable weather, human error, and technical malfunctions," the committee said in a statement.

Hours after the crash,the Polish government announced that there will be a presidential election before June in line with the country's constitution. According to the constitution, Parliament speaker Bronislaw Komorowski would take over presidential duties.

Tusk said Polish prosecutors were already in Smolensk and that he would probably host another cabinet meeting after returning to Warsaw late Saturday.

Komorowski declared a week of national mourning.

Some of the people on board the doomed plane were relatives of those slain in the Katyn massacre. Also among the victims was Anna Walentynowicz, whose firing in August 1980 from the Lenin Shipyards in Gdansk sparked a workers' strike that spurred the eventual creation of the Solidarity freedom movement. She went on to be a prominent member.

Kaczynski, 60, took office after winning an election run-off in October, 2005. Before that, he had been mayor of Warsaw, Poland's capital city.

The late president and his twin brother, Jaroslaw, were child movie stars who won fame in the 1962 movie "The Two Who Stole the Moon," about two troublemakers who try to get rich by stealing the moon and selling it.

Kaczynski is the first serving Polish leader to die since exiled World War II-era leader Gen. Wladyslaw Sikorski in a plane crash off Gibraltar in 1943.

Kaczynski, a Solidarity activist, became a senator in 1991 after serving as a representative to the National Assembly since 1989.

He had been the country's prosecutor-general and justice minister in a previous center-right government before being elected Warsaw mayor in 2002.

Kaczynski became well known for banning gay pride parades in Warsaw in 2004 and 2005, citing a lack of necessary documentation by organizers as the reason.

Kaczynski and Jaroslaw formed the socially conservative Law and Justice party in 2001 under the banner of developing the country's education and economy, fighting corruption and reforming rural areas.

According to the Aviation Safety Network, there have been 66 crashes involving Tu-154s, including six in the past five years. The Russian carrier Aeroflot recently withdrew its Tu-154 fleet from service.

Poland has long discussed replacing the planes that carry the country's leaders but said they lacked the funds.

The presidential plane was fully overhauled in December, the general director of the Aviakor aviation maintenance plant in Samara, Russia, told Rossiya-24. The plant repaired the plane's three engines, retrofitted electronic and navigation equipment and updated the interior, Alexei Gusev said. He said there could be no doubts that the plane was flightworthy.