The self-appointed government in Donetsk said in a statement on Thursday that the confirmed death toll from an accidental explosion at the Zasyadko mine had risen to 32.
It said one person remained unaccounted for, while 16 were receiving hospital treatment for injuries.
The explosion occurred before dawn more than 1,000 meters (3,200 feet) underground while some 230 workers were in the mine. Nearly 200 are reported to have been successfully evacuated.
Rebel officials said the accident was caused by methane gas exploding and was not connected with deadly fighting in east Ukraine's conflict pitting pro-Moscow separatists against government troops.
The city has been the target of frequent artillery fire, but a recent ceasefire has led to a reduction in fighting in the region.
Ukrainian safety officials say that 13 of the 99 deaths in the country's coal mines in 2014 were caused directly by fighting, with mines often being hit in artillery exchanges in the coal-rich region.
Accusations of negligence
The Kyiv government, which ordered a national day of mourning on Thursday with a minute of silence to be held at midday local time, has accused the rebel authorities of preventing 60 Ukrainian rescuers from providing assistance at the mine.
But a leading representatitve of the rebels, Denis Pushilin, told the insurgent-run Donetsk News Agency that no assistance had been offered by Ukrainian authorities.
"If we truly need assistance, we will turn to Russia," Pushilin was quoted as saying.
The Zasyadko mine in Donetsk has seen a series of deadly accidents in its 57 years of operation. One explosion in November 2007 claimed 101 lives, and two more the next month killed a total of 57.
A Ukrainian military spokesman has meanwhile said one government soldier has been killed and another wounded in continued fighting with the separatists over the past 24 hours, according to a Reuters report.
Another spokesman was quoted as saying the rebels had violated a ceasefire agreed last month with 40 attacks on military and civilian targets.
Interior Ministry Zoryan Shkiryak said the rebels were building up forces in southern Donetsk province near the government-held port city of Mariupol.
"There is no use in talking about a ceasefire from the side of the rebels. They are not withdrawing arms, they are not observing the ceasefire, they continue to relocation units and increase their number of tanks and rocket launcher," he said.
This comes as the United States continues to allege Moscow's active involvement in the conflict, with Assistant Secretary of State Victoria Nuland telling a foreign affairs committee on Wednesday that Russia had deployed "thousands and thousands" of troops to east Ukraine, and provided large amounts of miitary hardware to the rebels.
Moscow denies any involvement in the conflict, which has claimed some 6,000 lives over the past year.
It does, however, concede that some Russian soldiers may have volunteered to fight alongside the rebels while on leave.
tj/kms (AFP, AP, Reuters)