Death Toll Climbs to 44 in Istanbul Airport Attack

— -- The death toll from Tuesday's terror attack at Istanbul's international airport climbed to 44 today after a 25-year-old victim died in the hospital, Turkish authorities said.

The three attackers were from Russia, Kyrgyzstan and Uzbekistan, the Turkish prime minister's office confirmed to ABC News. A Turkish official said the Russian attacker was from the country's restive Dagestan region, the epicenter of an Islamic insurgency against the Russian state.

But they shared a home in Istanbul for the past month, according to Turkish officials, where they became inconspicuous during the several weeks they lived an apartment with a reinforced steel door, according to neighbors.

Neighbors described suspicious activity at the apartment, where they say the shades were always drawn shut.

One neighbor, who did not want to be identified, told ABC News there was a chemical smell coming from another apartment, and on Sunday the smell was so strong she thought there was a gas leak and called the landlord.

Meanwhile, 13 arrests were initially made in Istanbul after a series of overnight/early Thursday morning anti-terror raids, according to Turkey's Ministry of the Interior. Of those arrested, three were foreign nationals. Their nationalities were not identified and it was unclear whether the raids were directly linked to the attack. Then, on Friday morning, the number of arrested has jumped to 24.

The overnight operation consisted of 16 raids at different addresses in Istanbul, the ministry said. State-run media reported the addresses were in the city's Pendik, Basaksehir and Sultanbeyli neighborhoods.

No one has claimed responsibility for the attack but Turkey's interior minister has said "all findings show it’s ISIS." CIA Director John Brennan said Tuesday the attack "bears the hallmarks" of ISIS’ "depravity."

ABC News' Matthew McGarry and Engin Bas contributed to this report.