A Turkish opposition newspaper said police had boosted security at its offices after a tipoff it could be attacked by Islamic State group militants ahead of elections on Sunday.

Cumhuriyet newspaper said on its front page on Saturday it had been informed by police that IS suspects caught in Gaziantep near the Syrian border this week were carrying the address of its office in Ankara.

Police have sent extra officers and water cannon and set up barricades around the newspaper's headquarters in the capital and Istanbul.

"This newspaper has a history of publishing despite such threats," its executive board head Akin Atalay wrote in Saturday's paper.

"We are determined to carry on with our mission of covering news under any circumstances."

Security has been high in Turkey since a massive twin suicide bombing on a peace rally in Ankara on October 10 that killed 102 people in the worst such atrocity in the country's history.

Turkish prosecutors said Wednesday that a sleeper cell in Gaziantep working on the orders of the IS group in Syria had carried out the bombings to try to disrupt Sunday's election.

Cumhuriyet is a staunch opponent of the ruling Justice and Development Party (AKP).

Its editor-in-chief, Can Dundar, was threatened by President Recep Tayyip Erdogan ahead of the June 7 election after it published a story saying it had proof Turkey had sent arms to Islamist rebels in Syria.

Concerns over media freedoms in Turkey have heightened ahead of Sunday's election after riot police this week stormed the offices of two television stations critical of Erdogan.

There has also been a string of prosecutions of journalists, artists and even schoolboys accused of "insulting" the president.