KIEV, Ukraine -- A freight train derailed and released a cloud of toxic gas that sent at least 20 people to hospitals, an accident that touched nerves still raw more than two decades after the Chernobyl nuclear plant disaster.
Hundreds of people were evacuated and others fled their homes on their own after the Monday evening derailment sparked a fire in a cargo of yellow phosphorous, creating a cloud of gas that affected 14 villages in the former Soviet republic.
Twenty people were hospitalized, although their lives were not in danger, said Defense Ministry spokesman Ihor Halyavinsky. Authorities later said that six had been released, although media reports said other people in the area sought medical help.
"A disaster has happened. After the Chernobyl catastrophe we are dealing with (another) case that can pose a real threat for our people," said Deputy Prime Minister Oleksandr Kuzmuk, who went to the area in the Lviv region. "It is an extraordinary event, the consequences of which cannot be predicted."
He later backtracked on the remark, and other officials took pains to stress that the situation was under control and the danger minimal.
"The cloud of a toxic gas dispersed and there is no threat for people's lives," said Ihor Krol, spokesman for the Emergency Situations Ministry.
The train, en route from Kazakhstan to Poland, derailed near Lviv, and 15 of its 58 cars overturned, Krol said. Six of them caught fire and the poison cloud spread over a 35-square-mile area containing 14 villages, he said.
Rescuers extinguished the blaze. Phosphorus compounds are chiefly used in fertilizers, although they are important components of pesticides, toothpaste, detergents as well as explosives and fireworks. The highly toxic substance can cause liver damage if consumed.
Emergency workers sprinkled contaminated land with soda and sand and tried to cool off the cars, Krol said.
Residents were advised to stay inside, not to use water from wells, eat vegetables from their gardens or drink milk produced by their cows. Of the 11,000 people living in the contaminated area, 815 were evacuated, Krol said.
Media reports said other people had left the villages amid uncertainty about the effects of the accident.
On independent Channel 5 television, an elderly woman and a middle-aged man in one of the affected villages _ neither identified _ said authorities had not told them how to respond to the accident.
"Doctors did not come to our village. I only saw advice about what to do on TV," the woman said.
Concerns about the government response to such accidents still lingers from the 1986 explosion and fire at the Chernobyl plant in Ukraine, then a Soviet republic. The Soviet government kept the world's worst civilian nuclear accident under wraps for days and played down the disaster long afterward.
Transport Minister Mykola Rudkovsky said a commission was working at the scene to determine the cause of the rail accident. A criminal case was opened, which is standard practice in former Soviet republics, and state railway agency director Volodymyr Kozak said sabotage had been ruled out.
An alarm for heavy chemical pollution has been issued in the Lviv region, Ukraine, where yesterday evening a railway disaster led to a fire involving 15 containers of liquid yellow phosphorus. 

Extinguishing the fire proved extremely difficult because water cannot be used: in contact with phosphorus, water creates poisonous gas. It took six hours before the flames were extinguished. Gas was generated nonetheless, and at the moment the poisoned area extends about 90 sq. km. The casualties count is already heavy: 20 people are reported injured, 13 of them in critical condition. They have been carried to the Lviv hospital. ''Podrobnosti'' reports that the fire started when one of the containers started to leak and the phosphor caught fire.
Map highlighting Lviv and the Lviv Oblast.
The poisoned area includes 14 villages. From the five villages that are closer to the disaster area some 800 people have already been evacuated. Half of the evacuees had to manage on their own as there was not enough public transport for all.

At the moment there is no available data about the wind direction or next expected movements of the phosphorus cloud. Special firemen units remain on place to control the possibility of a new fire, while the administration of the Lviv Oblast tries to forecast the possible short- and mid-term evolution of the situation. 

The Ukrainian Railways have officially excluded the possibility of a terrorist act as a cause for the disaster.

''Podrobnosti'' reports the deadly dose of yellow phosphor at  0.1 g. According to that source, when poisoning living beings, phosphor causes liver necrosis and attacks the bones and spinal cord.