A fire at the Monte Carlo casino-hotel was caused by flying molten metal from a hand-held cutting torch used by workers who did not have proper permits, fire officials said Thursday.

Workers were cutting corrugated steel to set up window-washing equipment Friday at the casino on the Las Vegas strip but did not use proper mats to protect the roof, the Clark County Fire Department said. The first 911 call came from a passer-by.

If the contracting company, Union Erectors LLC, had applied for a permit, it would have been advised how to perform the work safely and likely been approved in four to five weeks, said Deputy Fire Chief Girard Page.

"It does take time and effort, but it's not that difficult," Page said.

Officials are reviewing whether to cite the contractor, which could result in fines of $1,000 and up to six months in jail per citation, a misdemeanor.

An attempt to call Union Erectors' Las Vegas office was unsuccessful.

The melted steel started a fire on the southwest corner of the main facade of the roof of the 3,000-room, 32-story hotel-casino Friday morning.

The flames spread quickly as they devoured a foam-like material on the facade. Thousands of guests and employees evacuated, but no serious injuries were reported. The fire was contained by about 120 fire personnel more than an hour after it began.

Construction workers using four hand-held extinguishers failed to put the blaze out, fire officials said.

The Monte Carlo remained closed Thursday. Casino operator MGM Mirage Inc. acknowledged that the paperwork for the metal work that caused the fire "did not meet our corporate standards" and said in a statement that the situation was "being immediately addressed."

Union Erectors had only a permit from the county to install window-washing equipment at the hotel, but not to conduct work with torches. A complete report on the investigation was still being compiled.

It was the first of two roof fires within a week at U.S. gambling resorts. A blaze Tuesday at the Great Cedar Hotel at Foxwoods Resort Casino in Mashantucket, Conn., also injured no one but forced guests to evacuate. That fire was traced to a malfunctioning device meant to keep pipes from freezing.

The Monte Carlo, which opened in June 1996, is on the Las Vegas Strip not far from the scene of Nevada's deadliest fire, a Nov. 21, 1980, blaze that killed 87 people at the old MGM Grand hotel and led to strict fire codes in Las Vegas resorts.