An accidental blast and lethal gas leaks at coalmines in Kazakhstan and Ukraine killed at least 53 people in the latest series of tragedies to hit the mining sector across the ex-Soviet Union.
In central Kazakhstan, an explosion and fire at a coalmine owned by giant steel maker Mittal left at least 40 dead.
"Forty miners died, three are in intensive care and one other is missing," a spokesman for the rescue team at the Lenin mine in Karaganda province said by telephone, adding that the rescue work was still going on.
The blast was caused on Wednesday by a build-up of methane gas about 500 metres below ground.
Rescue work was continuing but was hampered by a further gas leak in the area, the agency said. Several hundred other miners had managed to escape.
In Ukraine, a gas leak on Wednesday killed 13 miners and made dozens sick at the Zasyadko coalmine in the southeast of the ex-Soviet republic, officials said.
"Thirteen people died, 61 were injured and hospitalised. All the others are at the surface safe and sound," Mikhailo Korsakov, a spokesman for Ukraine's emergency situations ministry in the Donetsk region.
Kazakhstan's Lenin mine is part of a vast steel making complex in Karaganda and one of a number run in the former communist bloc by Mittal, the world's largest steel maker.
"We deeply regret this tragic accident and extend our full sympathy and condolences to the families of everyone that has been affected," the company's president Lakshmi Mittal said as quoted in the company's statement.
The statement said that Mittal would visit the site "this week" and pledged, "a full investigation will be launched into the causes of the explosion."