By Andrew Osborn and Peter Hobson

MOSCOW (Reuters) - At least 41 residents of the Siberian city of Irkutsk have died after drinking scented bath oil in a desperate search for an alcoholic high in one of the deadliest cases of its kind in years, Russian investigators said on Monday.

Use of counterfeit or surrogate alcohol is rife in Russia's regions, where two years of economic pain have pushed more people below the poverty line. Russian media reported that the victims were poor residents of Irkutsk, a hard scrabble city around 2,600 miles (4,000 km) east of Moscow.

The case underlines how hard up a large swath of the population is despite Moscow's growing profile and clout on the global stage.

"It is a terrible tragedy," Kremlin spokesman Dmitry Peskov told reporters. "This type of problem is well known and the president has been informed. Measures must be taken."

Russia's Investigative Committee sent a group of experienced investigators from Moscow, while Russian news agencies said the mayor of Irkutsk had declared a state of emergency and temporarily banned the sale of all liquids containing spirits not meant for human consumption.

"According to our latest data 41 of 57 people who were hospitalized after drinking the liquid have died," investigators said in a statement. "More than 2,000 units of the liquid have been confiscated with an overall volume of 500 liters."

Among liquids that have been used as a substitute for alcoholic drinks are perfume, after-shave, anti-freeze and window cleaner.

'DEADLIER THAN TERRORISM'

Alexei Navalny, a Kremlin critic who wants to challenge Vladimir Putin for the presidency in 2018, said the case had garnered wide attention because so many people had died at the same time. Hundreds of people, he said, died unremarked every day in unrelated cases for the same reason.

"The problem .... for Russia and its national security is roughly a thousand times more important than Syria, Aleppo, Ukraine and Trump put together," said Navalny, blaming poverty and corruption for the sale of such toxic surrogates.

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"Every year ... (such concoctions) kill more people than have been killed in terrorist attacks in Russia's entire history."

Investigators, who opened a criminal case into the poisonings, said they had detained two people suspected of distributing the deadly bath oil. The product carried a warning saying it should not be swallowed, but investigators said people had ignored that and consumed it as if it was alcohol.

The bath oil contained methylated spirit, they said, a toxic substance found in cleaning materials and paint stripper.

Police said they had found the workshop where the bath oil, called Hawthorn, was being produced alongside bootleg vodka.

Prime Minister Dmitry Medvedev said he wanted to look at banning products that could cause so many deaths and that the country's criminal code was being amended to toughen the punishment for people caught selling them.

Alcohol market expert Vadim Drobiz says up to 12 million Russians, or about one twelfth of the population, drink cheap surrogate alcohol.

(Additional reporting by Masha Tsvetkova and Elena Fabrichnaya in Moscow; Editing by Ralph Boulton)