Turkish President Recep Tayyip Erdogan has called on the Muslim world to unite against terrorism.

"As Muslims, we have an important mission which is to stand against organizations such as Daesh, Al Qaeda, Boko Haram, and al-Shabaab that do the greatest harm to Muslims by using the name of Islam," Erdogan said during an address at an event in Istanbul Sunday.

Erdogan said Muslims had a big role to play to protect their religion from exploitation. "If Muslims do not do anything to prevent these terrorist organizations, all those interventions targeting our region will continue," he said.

The president also criticized Russian presence in Syria. "If Russia had not seen Syria as a step to keep its presence in the East Mediterranean, there would have been a different policy to follow in the region," he said.

"What is Russia doing in Syria and Iraq? Do you know what is the answer? 'In line with the international law, if an administration invites you, then you can go there,' they say. You do not have to help a regime that killed nearly 400,000 people," Erdogan said while referring to Kremlin's support for the Bashar al-Assad regime.

Russia began its air operations in Syria on Sept. 30 to support Assad. While the Kremlin says the airstrikes target Daesh, some members of the western NATO alliance believe Russia is targeting groups opposed to Assad, including some that enjoy U.S. and Turkey's support.

According to a report released earlier this month by Amnesty International, Russian airstrikes in Syria have killed “hundreds” of civilians over the last three months.

- Parallel state probe

Erdogan also said the Turkish government would take concrete steps against the “parallel state” operating against the country.

"The parallel state emerged as an NGO in the country. We faced such a tough struggle [in fighting against the organization]. So, we need to take concrete steps against the organization. I hope the necessary steps will be taken in a period until 2019," he said.

The “parallel state”, known also by the initials FETO/PDY, refers to an organization purportedly led by Fetullah Gulen, a U.S.-based preacher accused of plotting to overthrow the Turkish government by infiltrating state institutions, including the police and judiciary.

The parallel state structure is also said to be behind a December 2013 corruption investigation into senior Turkish government figures, including ministers, and has been accused of wiretapping conversations, official misconduct, forgery plus the illegal acquisition and storage of personal data.

Since early 2014, investigations into the parallel state have seen hundreds of civil servants, including police and public prosecutors, arrested or reassigned.

Anadolu Agency