Massey Energy said exploratory teams have found a crack on the floor that could have allowed methane gas to seep in to the West Virginia mine where 29 men died on 5 April this year, in one of the nation’s worst mining disasters.

The crack was identified last week near the longwall but was not explored at the time to determine if it was the source of a methane explosion, Massey said.

Massey released a 2004 report on two instances when gas entered through cracks in the floor of the Upper Big Branch mine.

The crack and other potential sources in the mine now need to be fully examined before any conclusions can be reached, according to Massey.

The blast is the subject of a federal criminal probe and a civil probe.