While stressing the need for greater mine safety, U. S. President Barack Obama paid tribute on Sunday to 29 men killed in a West Virginia mine.

The president said at a service for the miners in Beckley, W. Va., "They knew there were risks, and so did their families. They knew their kids would say a prayer at night before they left. They knew their wives would wait for a call when their shift ended saying everything was OK. They knew their parents felt a pang of fear every time a breaking news alert came on or the radio cut in, but they left for the mines anyway."

Saying, "It was all for their families. These miners lived, as they died, in pursuit of the American dream," Obama praised the fallen miners for "all the hard work, all the hardship, all the time spent underground."

He had "seen the strength" of the coal mining community in a flood of letters and e-mails to the White House after the disaster, the president further said.

"Postmarked from different places, they often begin the same way: 'I am proud to be from a family of miners,' 'I am the son of a coal miner,' 'I am proud to be a coal miner's daughter.' They ask me to keep our miners in my thoughts. Never forget, they say, miners keep America's lights on. Then, they make a simple plea: don't let this happen again."

Vice President Joe Biden, West Virginia Gov. Joe Manchin and Sen. Robert C. Byrd, D-W. Va., also spoke at the service for the miners, killed in the explosion April 5 at Massey Energy's Upper Big Branch mine in Montcoal, W. Va.

A federal investigation of the worst U. S. mine disaster in nearly four decades has been ordered by Obama. (With Inputs from Agencies)