Turkish President Recep Tayyip Erdogan declared Saturday that Syrian President Bashar Assad was a "more advanced terrorist" than the Islamic State group, despite the deadly attack on Istanbul's Ataturk Airport that Turkish officials blame on IS.

Speaking in the town of Kilis near the border with Syria, Erdogan said the Syrian leader was responsible for the deaths of some 600,000 of his own citizens and was the root cause of the war in Syria.

"He is a more advanced terrorist than a terrorist from the PYD or the YPG," Erdogan said. "He is a more advanced terrorist than Daesh." Erdogan was referring to Syrian Kurdish militia, which Ankara accuses of being a terror organization because of their affiliation with Turkey's Kurdish rebels, and to the IS group by its Arabic name.

Three militants armed with assault rifles and suicide bombs attacked one of the world's busiest airports on Tuesday night, killing at least 44 people. Although no one has claimed responsibility for the attack, Turkish officials say they believe it was the work of IS.

Turkish authorities have detained at least 24 people in raids in several Istanbul neighborhoods over possible connections to the attack. Seventeen other people were detained in the province of Gaziantep, the state-run Anadolu Agency reported.

Erdogan paid an unannounced visit to the airport on Saturday, saying a prayer in front of a memorial set up for the victims, which features the pictures of airport employees killed in the rampage.

He later flew to Kilis, where the number of Syrian refugees is higher than the local Turkish population. IS militants have also attacked the town with cross-border rocket fire, killing 21 people there since January.

Erdogan said countries he did not name were supporting the Syrian Kurdish militia and the IS in a bid to prevent democracy in Syria and for their "dirty calculations" in the region. He also announced that his government would allow Syrian refugees in Turkey to take on Turkish citizenship.

Turkey has been accused of long turning a blind eye to jihadi fighters who crossed into Syria from Turkish territory in the hope that they would hasten Assad's downfall. Turkey has also been accused of not doing enough to fight IS, despite allowing the US-led coalition to use a key air base to conduct air strikes against jihadists.

Turkey denies the accusations but such statements from Erdogan help reinforce beliefs that fighting IS is not a priority for Ankara despite the extremist groups' attacks on Turkish territory.

Earlier, the Istanbul governor's office said 52 people were still in the hospital — 20 of them in intensive care — four days after the devastating airport attack. It said 184 airport victims had been discharged from hospitals so far, including 13 people released Saturday.

Prosecutors have established the identity of two of the three airport attackers — giving their names as Rakim Bulgarov and Vadim Osmanov — and were trying to identify the third, Anadolu said. Other media reports have given different versions of Osmanov's name.

Investigators' attentions have reportedly focused on whether a Chechen extremist known to be a top lieutenant in the Islamic State group masterminded the attack.

US Rep. Michael McCaul, chairman of the House Committee on Homeland Security, told CNN that Akhmed Chatayev directed the attack. The CIA and White House declined to comment on McCaul's assertion and officials said the investigation into the airport bombings is still ongoing. McCaul could not be reached for further comment.

Turkish officials also were not able to confirm Chatayev's possible role in the deadly attack. The Sabah newspaper, which is close to the Turkish government, said police had launched a manhunt for him.

The Islamic State group, which has used the porous border with Turkey to establish itself in neighboring Syria and Iraq, has repeatedly threatened Turkey. In turn, Turkey has blamed IS for several major bombings in the past year in Ankara and Istanbul.

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Fraser reported from Ankara, Turkey. (**)