Poland's Prime Minister Donald Tusk said on Saturday that he would travel immediately to Smolensk, western Russia, where Polish president Lech Kaczynski and other elite officials died in a plane crash.
"In a moment I will go to Smolensk, there are Polish prosecutors there already," Tusk said in Warsaw after an emergency cabinet meeting in the wake of the devastating crash.
"There may be another cabinet meeting after I return this evening."
"This kind of dramatic tragedy is unheard of in the modern world," the prime minister added.
Poland's acting head of state declared a week of mourning after the crash Saturday in Russia of a Polish government plane which killed the president and scores of other officials.
"We are united -- there is no (political) left or right -- we are united in national mourning," said Bronislaw Komorowski, Poland's parliamentary speaker who took charge of presidential duties after Kaczynski's death.
Kaczynski and other senior Polish officials died when their plane crashed in thick fog while attempting to land in the western Russian city of Smolensk on Saturday morning.
They were due to attend ceremonies marking the 70th anniversary of the WWII Soviet slaughter of 22,000 Polish officers in the nearby Katyn forest and elsewhere in Russia and Ukraine.