MEXICO CITY • Mexican army divers were blocked by debris in their first attempt to descend deep into a flooded coal mine in northern Mexico where 10 miners have been trapped for a week, the country’s defense minister said on Thursday.

The miners became trapped at a mine in the border state of Coahuila on Aug. 3 when their excavation work caused a tunnel wall to collapse, triggering flooding in parts of the underground mine.

Mexican officials by Thursday had managed to dramatically reduce water depths that initially had topped about 100 feet but have struggled to send in rescue teams even on preliminary efforts to gauge whether conditions would be safe for a rescue mission.

Two military divers entered one of the three flooded mine shafts on Wednesday after a miner and a rescue professional submerged four times to clear debris, but were unable to fully enter the mine.

“It had been blocked,” Defense Minister Luis Cresencio told a news conference on Thursday.

“They don’t have the necessary visibility to identify what they’re finding,” Cresencio said.