The conflict has killed an estimated 6,400 people since April 2014, according to the United Nations.
The announcement represents the first time prosecutors have confirmed possible physical evidence of a missile bringing down the plane and killing all 298 people on board.
With fighting surging again near the main separatist stronghold, only one of the corridors has been left open in the two separatism-plagued regions of Donetsk and Luhansk.
The fire, which erupted late Monday at the depot near the village of Hlevaha just southwest of Kiev, has filled the skies with plumes of black smoke.
Ukraine’s General Staff said in a statement that rebels deployed around 1,000 fighters and dozens of tanks and self-propelled artillery systems.
Russian defence officials lashed out at the US, accusing it of undermining global security by funding revolutions and expanding NATO in a bid to contain Russia.
Peace talks continue between Ukraine and Russia, fights continue on ground.
There is bipartisan support in Congress to provide the arms to Ukrainian forces battling the rebels.
Both sides in the conflict have given assurances they are complying with pullback requirements.
The blast occurred before dawn Wednesday more than 1,000 meters (3,200 feet) underground at the Zasyadko mine in Donetsk.
Separatist authorities in Donetsk said in a statement that the blast occurred at a depth of more than 1,000 meters.
Kerry said he hopes the ceasefire will be implemented fully “in the next hours, certainly not more than days.”
Ultra-nationalist organisation Right Sector said that one of its fighters was also killed in the attack.
The deaths of the 3 Ukrainian soldiers came after a two-day lull in clashes with the pro-Russian separatists.
“If no new funds are received from Kiev, then naturally we cannot continue delivering gas to Ukraine,” said Sergei.