Officials rule out rail car as cause of deadly U.S. fertilizer plant explosion

U.S. officials on Tuesday ruled out a rail car loaded with ammonia nitrate as the cause of a deadly fertilizer plant blast that virtually leveled the small Texas town of West.

Assistant Texas Fire Marshal Kelly Kistner told a press conference in West that the rail car wasn't the cause of the fire, but rather a "victim" of the fire and subsequent explosion, according to local newspaper The Houston Chronicle.

On Monday, Bryan Shaw, chairman of the Texas Commission on Environmental Quality, raised the possibility the explosion may have been triggered by the rail car.

"It's more likely -- as I've done some analysis of that -- that it's likely possibly a rail car with ammonium nitrate in it," he said.

A policeman stands guard on the blast site in West, Texas, the United States, on April 21, 2013. (Xinhua/Michael Ainsworth)

The powerful explosion occurred around 7:50 p.m. local time last Wednesday at the fertilizer plant in West, a small town about 320 km north of Houston.

The blast killed at least 14 people and injured about 200 others. Another 60 remained unaccounted for in the blast, local officials said.

A memorial is planned on Thursday, which U.S. President Barack Obama and First Lady Michelle Obama will attend.

Authorities said they were still investigating the cause of the explosion.

Kistner said Thursday that officials have yet to determine the exact cause of the blast and still don't know how much ammonia nitrate was being stored at the facility at the time of the disaster.

Investigators were trying to find the first heat source and where the fire started, Kistner said.