Two people, among them a police officer, were killed and 15 others were wounded in Sunday's terror attack in Kharkov, the Ukrainian Interior Ministry said on its website.
There are five law enforcement officers among those wounded in the explosion, it said.
The regional prosecutor's office earlier reported that three people were killed.
A blast went off during a peace march at about 1:20 p.m. on Sunday, the Interior Ministry said. Several public events had earlier been scheduled for Sunday, including a peace march, it said.
Ukraine's Security Service (SBU) has already detained four suspected organizers of a blast, said SBU spokesman Markiyan Lubkivskiy.
"The Ukrainian Security Service has detained four persons, who might have played a role in organizing and carrying out terrorist crimes in Kharkov, including an explosion which killed two and wounded eight citizens," Lubkivskiy wrote on Facebook on Sunday.
Lubkivskiy later said that several terror attacks, scheduled for Sunday, had been prevented in Kharkov.
"Four people were detained in the act of preparing an attack with a Shmel flame thrower on a club, visited by volunteers and soldiers who took part in the counterterrorism operation, and on a shopping center. Other subversive and terror attacks have been prevented, as well," he said.
The seized Shmel flame thrower was made in Russia, he added.
"In connection with the bombing and attempts to carry out other terror attacks, the Ukrainian Security Service has announced the highest terror alert in Kharkov. Law enforcement services have combined their efforts in taking large-scale emergency counterterrorism measures," he said.
Secretary of the Ukrainian National Security and Defense Council Oleksandr Turchynov said earlier that a counterterrorism operation had been launched following Sunday's bombing.
A criminal inquiry has been started on terrorism counts. The inquiry will be conducted by the Ukrainian Security Service.
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