Khazakstan's president Nursultan Nazarbayev defended safety standards at the Karaganda mine, owned by giant steelmaker Mittal, where an explosion and fire left at least 41 dead.
"The equipment and safety norms have in recent years reached a very high level ... Despite that, foreseeing an accident like this is impossible. The miners know it," Nazarbayev said.
The blast was most likely caused by a build-up of methane gas about 500 metres below ground.
Meanwhile in Ukraine, a gas leak killed 13 miners and made dozens sick at the Zasyadko coal mine in the country’s southeast.
Ukraine's emergency situations ministry blamed a sudden leak of a mixture of coal and gas for the accident, which killed the miners as they worked about a kilometre underground.
Deadly legacy
The double-tragedy underlines the safety troubles affecting huge, ageing mines of all types across the Soviet Union.
Earlier this month, 25 miners died in a fire at a British-owned gold mine in Russia's Siberian region of Chita, sparking allegations that profits had been put before safety.
Kazakhstan's Lenin mine is part of a vast steelmaking complex in Karaganda and one of a number run by Mittal, the world's largest steelmaker. Coal is a vital raw material in the steel-making process.
The company issued a statement that it will conduct a full investigation into the causes of the explosion.
The mine has had several previous problems, including an explosion in December 2004 blast that killed 23 miners.
Ukraine's Zasyadko mine is also a major facility with a deadly history.
In 1999 an explosion there claimed 50 lives, in 2001 another explosion claimed 55 lives and in 2002 another blast claimed 20 lives.
The mine employs some 10,000 people and produces between 8,000 and 10,000 tonnes of coal every 24 hours.