The sacked head of Ukraine's air force has been arrested along with three other top military officials after Saturday's crash at an air show in Lviv which killed 83 people.
The defence minister has offered his resignation, which the president is considering.
Families of the victims are still anxiously waiting at the city morgue and hospitals in Lviv as officials try to identify the remains of those killed.
Monday has been declared a day of national mourning in honour of those who died in what is the world's worst air show disaster.
People watched in horror on Saturday as a fighter jet performing acrobatic manoeuvres apparently clipped trees and span out of control, ploughing into the spectator stands.
President Leonid Kuchma's administration appears to hold the military responsible for the disaster, accusing officers of poor organisation and negligence.
Within hours of the crash, Mr Kuchma had sacked the commander of the air force, General Viktor Strelnikov, and General Sergei Oniszhenko, the head of the 14th air force division which had been putting on the show.
Now the two men have been arrested along with two other officers involved in the planning of the show.
They are suspected of a "negligent attitude to the military service that led to heavy consequences".
Expert says the charge is a euphemism for sloppy safety procedures that allowed pilots to perform their stunts too close to the public.
The two pilots of the jet, who ejected safely before it hit the crowds, could also face arrest once they have recovered from their injuries.
It is not yet known whether Mr Kuchma will accept the resignation of Defence Minister Volodymir Shkidchenko.
A massive cloud of smoke rose from the crash site
But Chief of Staff Petro Strulya, who was deputising for Mr Shkidchenko at the time of the crash, has already been sacked.
Our correspondent says Mr Kuchma's decisive action is in sharp contrast to his response last October when a Russian jet plunged into the Black Sea after being hit by a Ukrainian army missile.
That time his administration initially denied the military's responsibility, drawing strong criticism.
On Monday, Ukrainians will observe a national day of mourning for the 83 victims, 19 of them children.
So far, officials have identified 68 bodies but the severity of the injuries has made the process difficult.
Traumatised relatives have been thronging the morgue in Lviv, trying to find out if their loved ones are among those killed.
"These days have been the most terrible days of my life," a woman called Lyudmila told Reuters news agency.
"Yesterday my daughter and son-in-law went to the air show and since then I haven't heard anything about or from them".
Olga Dudchenko, whose seven-year-old daughter and husband died in the crash, said: "I can think of nothing that could relieve my grief".
(China Daily July 29, 2002)