Russian investigators said on Tuesday they had opened a criminal case into a senior regional official in Siberia after at least 77 people died from drinking bath oil for alcoholic kicks.

The mass poisoning in Irkutsk, a city 2,600 miles (4,000 km) east of Moscow, was the worst of its kind in recent years in a country where up to 12 million people consume cheap surrogate alcohol.

Investigators have so far detained 23 people and President Vladimir Putin has demanded tighter controls on the production and sale of drinks, medicines, perfumes and other liquids with a high percentage of ethanol, or drinkable alcohol.

The lethal bath oil in Irkutsk was contaminated with methanol, a related form of alcohol which is poisonous.

Russia's Investigative Committee said on Tuesday that Yevgeniya Nefedova, a deputy minister responsible for the use of land belonging to the Irkutsk regional government, had been charged with negligence over the affair.

In November, a month before the poisoning, Nefedova had been passed evidence that a plot of state land was being used to sell illegal alcohol, investigators said.

"She had all the powers and justification to ask a court to annul the (rental) contract ... But instead Nefedova only signed off on another fine," the statement said.

The Irkutsk region's health ministry meanwhile said that the number of deaths from the poisoning had risen to 77 and that 16 people remained in hospital.