Four missing West Virginia miners are found dead

The explosion was the US coal mining industry's worst for 40 years

The bodies of four missing miners have been found in West Virginia, taking the death toll to 29 and making it US coal mining's worst accident in 40 years.

Difficult conditions had hampered rescuers in their search for survivors after Monday's underground explosion at the Upper Big Branch mine.

Relatives had hoped the four miners had sought refuge in one of the mine's airtight chambers after the blast.

A rescue crew earlier reached one of the chambers, but found no-one there.

Speaking shortly after the discovery, West Virginia Governor Joe Manchin said: "The journey has ended."

US MINE DISASTERS Jan 2006 - 12 killed in methane explosion at Sago mine, Tallmansville, West Virginia 2001 - 13 dead in explosions in mine at Brookwood, Alabama 1989 - 10 killed in explosion at Wheatcroft, Kentucky 1984 - 27 killed in fire at Orangeville, Utah 1970 - 38 killed in explosion at Hyden, Kentucky 1968 - 78 killed in explosion at Farmington, West Virginia 1907 - 362 killed in explosion at Monongah, West Virginia Battle raging in US mining country

The bodies of 18 other dead workers remain inside the damaged mine, 50km (30 miles) south of Charleston.

President Barack Obama earlier offered his condolences to the families of the victims, and said he wanted federal mine safety investigators to report next week on the cause of the explosion.

As details emerged of prior safety violations at the Upper Big Branch mine, owned by Massey Energy Company, Mr Obama said steps needed to be taken to prevent similar accidents.

The latest death-toll makes it the worst coal mine disaster in the US since 38 people were killed in a Kentucky mine in 1970.