An explosion on Sunday, the second in as many days, killed four men in the same colliery in eastern Ukraine hit by the country's worst mining accident two weeks ago.
Ukraine's Mining Inspectorate said one man was missing.
The inspectorate said the four dead in the 9 p.m. blast were maintenance workers trying to clear the affected section, more than 1 kilometre underground at the Zasyadko mine in Donetsk.
Thirty-seven miners were helping the maintenance team and all but one had been brought to the surface. Rescue teams were searching for the missing man.
An explosion struck the same section on Saturday morning. More than 60 men in the area were taken to the surface.
More than 40 were being treated in hospital in Donetsk, in the heart of the Donbass coalfield.
A methane blast on November 18 killed 101 miners at Zasyadko and more than 40 miners were still receiving hospital treatment from that accident. Fires are still burning in the affected area and about 10 bodies have still to be recovered.
All production of coal has stopped at Zasyadko, described by industry officials as one of the most technically advanced and profitable mines in Ukraine. Four major accidents have struck the pit since 2001.
Interfax Ukraine news agency, quoting local officials, said acting Prime Minister Viktor Yanukovich, heading a caretaker administration pending nomination of a post-election government, would travel to Donetsk on Monday.
Deadly accidents regularly strike the ex-Soviet state's collieries, many of which date from the 19th century. Experts say the practice of extracting coal from seams far below the surface increases the risk of methane explosions. ( Reuters )