Washington, Apr 11 (DPA): US President Barack Obama vowed the government would conduct a thorough investigation of the country's worst mining accident in decades after the bodies of four missing US miners were found early Saturday.

The final death toll stood at 29.

"We did not receive the miracle we prayed for," said West Virgina Governor Joe Manchin. "This journey has ended and now the healing will start."

There had been fading hope Friday of finding survivors four days after an explosion at the Upper Big Branch mine, but teams made last attempts reach a rescue chamber that would have offered the miners safety.

"It is with a heavy heart that we learn the news that the last four missing miners did not survive the explosion in the Upper Big Branch mine," Obama said in a statement Saturday.

"My thoughts and prayers are with the families of all those who were lost in this tragic accident, and my gratitude goes out to the rescue teams who worked so tirelessly and heroically to search for the missing."

Obama vowed a thorough investigation and accountability. "All Americans deserve to work in a place that is safe, and we must take whatever steps are necessary to ensure that all our miners are as safe as possible so that a disaster like this doesn't happen again," he said.

Obama had earlier said he was "praying for a miracle" and was in "awe of the courage and selflessness shown by rescue teams that risked their lives over and over."

The accident was possibly caused by a mixture of volatile methane gas and coal dust. The mine had been repeatedly cited for violations that allowed methane and other poison gas build-ups.

Obama was to meet next week with Labour Secretary Hilda Solis and Mine Safety and Health Administrator Joe Main to find out "what went wrong and why it went wrong so badly" in West Virginia.