The victims had gathered to celebrate the life of famous poet Pir Sultan Abdal when angry protesters surrounded and attacked the hotel.

Thousands of people carrying photos of the victims – which included many leftists, writers, artists and intellectuals – held a march on Thursday and gathered around site of the former Madimak Hotel, which is now a state science and culture center.

Turkish media reports said the leader of main opposition Republican People's Party (CHP) Kemal Kilicdaroglu and his wife Selvi would attend the commemoration with a delegation.

Earlier in the day, Sivas Governor Alim Barut and Acting Mayor Erdal Karaca visited the site with other officials and laid carnations in memory of the victims.

"July 2, 1993 is marked in Sivas residents' memory as a black day with full of grief," said Barut, adding that the fire at the hotel also set fire to the future of Sivas.

Hidayet Yildirim, the head of Pir Sultan Abdal Cultural Association, said it was essential to make Madimak Hotel a "shame museum" to recognize the Alevi community's demands for democracy and justice.

"Our hearts are once again filled with grief and pain on the 22nd anniversary of the massacre at Madimak," Yildirim said in Sivas' Cumhuriyet Square.

In July 2014, Turkey presidency's State Auditing Board (DDK) issued a report that found grave negligence by the state in the handling of the incident.

According to the report, Turkey failed to take adequate safety precautions in the region to prevent this social crisis that could have been clearly anticipated considering the profile of the demonstrators.

The operation was carried out in 18 different cities including Ankara, Eskişehir, Çorum, Orduand Sivas. The operation was launched by the Sivas Police Department.

According to some media sources as part of the operation, the number of detainees might increase to 35 during the day.

Dozens of officers, including senior police officers, were arrested in connection with similar charges in 2014.

The suspects are accused of listening to conversations of thousands with the supposed intention of creating a coup; high-level officials were believed to have been wiretapped for this aim.The perpetrators are supposedly part of the Fethullah Gülen-led group, which is considered a terrorist organization by the government..

The Gülen-led group has been accused of being a large international-scale network which has tapped Turkish officials, including their encrypted phones. The network runs private schools in more than 160 countries, including the U.S., Europe, Asia and Africa. THe network has faced suspicion  in countries such Russia, Azerbaijan, Germany and the U.S. Their aim is supposedly to bring down Turkey's newly elected government.

The bus accident ended in a crash into a water mountain on the roadside, according to a witness.

The bus, en route from the province of Istanbul to the eastern province of Ağrı, pursued sliding on its sliding after flipping and only could stop when it slammed into the water fountain.

The injured were immediately hospitalized after the accident. At least four passengers were said to have been in critical condition.

The driver suffered no injuries and was taken into custody by police. An initial investigation said the front tires of the bus were not the right type for the winter season.

Winter tires are a requirement for all heavy vehicles in Turkey, including trucks, tow trucks, tankers and buses.

Officers took security precautions on the spot after receiving the suspicious envelope, which only read Great Britain as the return address and the police station as the receiver.

An emergency squad from AFAD immediately responded to the police station’s call. Masked experts in special outfits, conducted first tests on the envelope, which claimed to contain an unknown substance, without opening it.

The two postmen on motorcycle, who were assumed as being exposed to the powder suspected to be inside the closed envelope, have been held for observation at the hospital of the Cumhuriyet University Medical Science Faculty after an initial examination at a province hospital.