At least 35 people have died from drinking bootleg sugarcane liquor laced with methanol in the past week, and nearly 600 have fallen ill — overwhelming hospitals in Nicaragua's worst health crisis in recent history, officials said Monday.

Health officials warned the death toll would likely rise. It is believed that at least a dozen deaths have not been registered yet, said Dr. Humberto Martinez, assistant health director in the city of Leon, where most of the cases have occurred.

Methanol is a toxic industrial alcohol often used in antifreeze that even in small amounts can cause blindness and death. Bootleggers sometimes add industrial alcohol to strengthen home-brewed liquor.

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Meanwhile, police have arrested six people in connection with the lethal bootleg. Officials also seized 17,200 gallons of unauthorized sugarcane liquor, known as "aguardiente," said Mario Perez Cassar, head of civil defense.

TheU.S. Southern Command flew in 25 health experts, medicine and equipment Sunday to help treat the victims in Leon, 45 miles west of the Nicaraguan capital of Managua.

So far, 603 cases have been reported across the country since last week, Martinez said.

The federal government called a national emergency and transferred staff from the capital to hospitals in Leon last week. Authorities also banned the distribution and sale of distilled alcohol, though bottled liquor that has been sealed with a government health inspection sticker can still be sold.

Many poor Nicaraguans drink home-brewed sugarcane alcohol, which at about $1 per quarts is cheaper than legal, taxed alcohol.

Miurell Gamez, head of health services in Leon state, said tests revealed the victims had high concentrations of methanol in their blood and suffered from headaches, dizziness, nausea and vomiting. Many will be left permanently blind, health officials said.

Leon Mayor Transito Tellez called three days of mourning for the city.

In neighboring El Salvador, methanol-tainted alcohol killed more than 100 people in 2000.