Turkish security forces detained hundreds of members and supporters of the PKK terror group, the Interior Ministry said Sunday.

Some 735 suspects were apprehended Friday as part of 156 operations across Turkey, the ministry said.

The suspects were planning to organize massive demonstrations to mark the 20th anniversary of the capture of the imprisoned leader of the PKK, Abdullah Öcalan, who was detained in Kenya on Feb. 15, 1999, as well as to spread chaos ahead of March 31 local elections in Turkey.

The security forces also seized six long-barreled guns, 32 hunting rifles, 14 heavy weapon ammunition, 19 handguns, other various ammunitions, 1 hand grenade, 20 kilograms (44 pounds) of TNT, 225 kg of ammonium nitrate, 16 mines and improvised explosive devices.

Sixty-one of the detained were later arrested, while 226 were freed.

Öcalan, who is being held on an island prison in the Sea of Marmara where he serves the life sentence he was handed down in 2002, remains a key figure for the terrorist group. PKK supporters used to hold mass rallies eventually descending into violent riots in past years to mark the anniversary of his capture. This year, apart from a few small-scale rallies interrupted by police, the group's supporters, including members of the Peoples' Democratic Party (HDP), organized no major events thanks to strict security measures.

Formed in 1978, the PKK terrorist group has been fighting the Turkish government for an independent state. Its terror campaign has caused the deaths of more than 40,000 people. The PKK is listed as a terrorist organization by Turkey, the U.S. and the European Union.

The PKK resumed its decades-old campaign in July 2015 after a three-year cease-fire collapsed. Since then more than 1,200 people, including security personnel and civilians, have lost their lives in PKK attacks.