ABAI, Kazakhstan, Jan 12 (Reuters) - Hopes are fading of saving 23 miners trapped in the Abaiskaya mine in central Kazakhstan were at least seven died in an explosion on Friday, but the rescue operation will continue.

Kazakh Deputy Prime Minister Umirzak Shukeyev told reporters on Saturday that rescue workers had halted their search because of the high level of methane concentration at the mine.

"The chances that the 23 miners are alive are slim but there is still hope, and we will do everything necessary to save them," he said.

The rescue operation at the mine, owned by the world's largest steel maker, Arcelor Mittal <MT.N> <ISPA.AS>, is complicated by an underground fire.

Nurlan Nigmatulin, a regional governor, said three days of mourning will be announced in the Karaganda region on Jan. 14-16 for those who died in the explosion.

An explosion at another mine owned by Arcelor Mittal in the same region, the Lenin mine, killed 43 workers in 2006. Two earlier blasts, in 2002 and 2004, killed more than 30 miners.

Coal mining accidents occur frequently in the former Soviet Union, where safety practices are often less strictly observed than in Western mines.

Explosions in coal mines are most often the result of a build-up of methane gas, although emergency officials did not confirm the cause of Friday's blast. (Reporting by Sergei Tereshchenko; Writing by Maria Kiselyova in Moscow; Editing by Ibon Villelabeitia)

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