An explosion at a mining complex in northeastern Mexico killed three workers and critically injured six others, authorities said Sunday.

A towering, external oven used to extract metals and mix iron alloys exploded Saturday night at a ferromagnesian mining plant operated by Compania Minera Autlan SA in Tomas, in the Gulf coast state of Veracruz.

Two workers sustained burns over most of their bodies and died instantly. A third died while being transported to the hospital, said Aldo Elias, a spokesman for investigators in Panuco, a city encompassing Tomas and the mining complex.

Elias said six other workers were severely burned. They were taken by the Red Cross to hospitals in Tampico, in Tamaulipas state. The mining complex is located about 355 miles north of the port city of Veracruz.

CountryWatch: Mexico

Workers reached by telephone at the mining complex in Tomas said that, while there is a mine onsite, the explosion occurred above ground in an area containing 11 ovens.

David Davilla, one of the plant's managers, said at least 400 workers were employed at the complex, but refused to confirm how many were evacuated because of the explosion.

Compania Minera Autlan said it was preparing a statement, but that it might not be released until Monday.

Ranulfo Marquez, deputy director of state civil protection authorities, confirmed the deaths and injuries, lowering initial estimates.

Marquez originally said the blast may have been caused by the mishandling of explosives within the mining complex, but investigators later said explosives weren't used at the site and speculated the blast may have been caused by a buildup of gas and pressure around the oven.

Ferromagnesian is a metallic compound containing iron and magnesium.

Mexico's mining industry has been under intense scrutiny after a February explosion that killed 65 workers at the Pasta de Conchos coal mine in northern Mexico.

The disaster was followed by a scandal that has rocked the national miners' union. The union's top leader, Napoleon Gomez, was nominally replaced and is being investigated for possible mismanagement of a $55 million fund. Much of the union has refused to recognize the change in leadership.

Gomez is in hiding and the office of President Vicente Fox said last week that Mexico has sought the help from an international police organization in finding and arresting him.

But the Mexican media, including the government new agency Notimex, reported Sunday that a judge had thrown out one of numerous arrest warrants against Gomez.

Judge Ranulfo Castillo ruled there wasn't sufficient evidence to support an arrest warrant for money laundering sought against Gomez by the federal attorney general's office, Mexican newspapers reported. A spokesman for federal prosecutors said he had no knowledge of the ruling and court officials could not immediately be reached for comment.

The pre-dawn explosion Feb. 19 at the Pasta de Conchos coal mine near San Juan Sabinas, south of the Texas border, had sparked temperatures that reached 1,110 degrees Fahrenheit and released heavy amounts of methane gas and carbon monoxide.

Family members waited nearly a week for news of those trapped underground before mining company officials confirmed that none could possibly have survived. Rescue teams are still working to recover the bodies of those killed in that explosion.