Thirty-three people have died this week in Istanbul after consuming adulterated alcohol, while another 48 have been hospitalised, according to the Turkish state news agency Anadolu.
Police seized over 30,000 litres of the illegally produced alcohol during a raid.
Authorities in Istanbul announced on Thursday evening that four people had been arrested on suspicion of involuntary manslaughter.
The clandestine production of alcohol in Turkey has surged due to an explosive increase in taxes on alcoholic beverages.
Raki, the national drink, costs around 1,300 Turkish lira (about €35) per litre in supermarkets, in a country where the monthly minimum wage is no more than 17,000 lira (€465).
Experts say methanol is often used in adulterated alcohol instead of the more expensive ethanol, and this leads to poisoning.
