A fire started on Tuesday at a warehouse in a military base in Ukraine's central Vinnytsia, setting off a series of explosions which forced 30,000 people to evacuate the premises.
About 188,000 tons of munitions were kept at the depot in the town of Kalynivka, 190 kilometers southwest of capital Kiev, including rockets for the Grad multiple grenade launchers, according to local sources.
Firefighters on Thursday morning were still unable to put out the blaze because there were still periodic explosions at the site, said Mykola Chechotkin, chief of the Ukrainian State Service for Emergency Situations.
"Explosions are still happening as you can hear," he told reporters in Kalynivka. "It's too dangerous for firefighters to access the area even though four fire tanks are working there."
Anatoliy Matios, the country's chief military prosecutor, denied earlier statements from authorities suggesting that a group of foreign saboteurs may have set the depot on fire.
Matios said investigators were looking into possible negligence, abuse of power or sabotage by those who were authorized to handle the munitions.
He also said investigators discovered that the fire alarm at the depot was not working and that its security force was understaffed.
"Neither did the investigators, nor the Security Service, nor any law enforcement agencies find any groups of saboteurs in the Vinnytsia region that people are talking about on Facebook," Matios said.
He was apparently referring to comments made by several senior Ukrainian officials on social media Wednesday, blaming Russian saboteurs for the fire.
Media sources have reported four large fires at ammunition and weapons depots in Ukraine since 2015.
Matios said it will be hard for the government to restore the military reserves that have been destroyed by explosions over the past two years.
Kiev officials said the destruction of two ammunition depots this year have dealt the biggest blow to the country's combat capability since the start of the conflict in eastern Ukraine.
"The country has suffered the biggest blow to our fighting capacity since the start of the war," the secretary of the Ukrainian Security and Defense Council, Oleksandr Turchynov, told journalists.
"There are many violations of fire and air safety at our arsenals. And these are the consequences," Turchynov said. "We've shown that we're not capable of protecting our strategic arsenals."
Both Matios and Turchynov said Ukraine's General Staff, which is responsible for the military's day-to-day operations, should be held accountable for security failings at the depots.
In a post on Facebook, Chief of the General Staff Viktor Muzhenko denied accusations that his institution was incompetent.
The comments, he said, were intended to sow doubt about the armed forces' ability to protect the country, and undermine trust in the army.
The explosions come as Ukraine's military is engaged in a grueling war with pro-Russia fighters seeking greater autonomy in eastern regions, which has been going on for more than three years now.