Crucial safety equipment was disabled weeks before an explosion at the Upper Big Branch mine in the US killed 29 miners on 5 April, it has been alleged.

According to miners who survived the accident, on 13 February a methane gas monitor on a continuous mining machine was disabled after the monitor repeatedly shut down the machine due to high methane concentrations, according to NPR News.

The methane monitor is designed to signal a warning and automatically shut down the machine when gas approaches dangerous concentrations, forcing immediate evacuation.

Massey Energy, owner of the West Virginia mine, said the malfunctioning detector was disabled while the equipment was being moved to a less volatile part of the mine.

The US Mine Safety and Health Administration said in a statement that any allegation of tampering with methane detectors is deeply troubling and such actions would clearly violate the law and would jeopardise the lives and safety of miners.

Meanwhile, difficult working conditions in the mine have slowed the investigation into the explosion and a report on the accident could be delayed until the end of the year.

Federal and state agencies have been gathering evidence inside the mine and have jointly conducted 126 interviews so far.