Turkish flags, with the control tower in the background, fly at half mast at the country's largest airport, Istanbul Ataturk, following the blast in Istanbul, Turkey, June 29, 2016. [Photo/Agencies]

Cracks in the international alliance against terrorism, particularly countries' inability to even agree on what constitutes terrorism and who is a terrorist, are compromising efforts to combat it.

The horrific terrorist attack on Istanbul's Ataturk Airport, which left 44 people dead and almost 240 injured, has tragically highlighted this once again.

The three suicide attackers have reportedly been identified as being Russian, Uzbek and Kyrgyz nationals, and Ahmed Chataev, a Russian citizen of Chechen origin, has been identified as the mastermind behind the atrocity.

That Chataev has long been wanted by Russia on terrorism-related charges but remained free as he enjoyed European protection testifies to the gaping hole in the international community's collective defense against terror, which Chataev and others are taking advantage of.

Chataev was put on a wanted list in Russia in 2003 for allegedly sponsoring terrorism and recruiting extremists. But he received asylum in Austria the same year, thanks in part to his claim that he lost an arm to torture in a Russian prison and was being persecuted in Russia.

The European authorities' faith in Chataev's innocence has been amazing considering the Russian warnings that Chataev had a "leading role" in training extremists for planned terrorist attacks in Russia and Western Europe, and obvious past clues of his links to terrorism.

Although he repeatedly escaped extradition with his refugee status, he finally made it onto the US Justice Department's terrorist list in 2015 for his role in recruiting extremists. According to the United Nations Security Council, he now has 130 terrorists at his disposal in Syria.

That Chataev has remained at large and was able to plot such an attack despite his role as a high-profile terrorist being apparent is more than just an embarrassment for the international community: It remains a mystery precisely why anti-terror agencies in related countries have been so ineffective in monitoring such a key terrorist suspect, particularly after he was identified as a terrorist by both the UN and US.

But the evident disagreement between Russian and European authorities over whether Chataev qualified as a terrorist obviously created the room in which he has been able to operate.

The attack on Ataturk Airport, Saturday's hostage crisis in Bangladesh, along with the latest threat by the Islamic State group to attack London's Heathrow airport around the US' Independence Day, should serve as an emergency call for true international solidarity in the fight against terrorism.

The international community must not let different definitions of terrorism and terrorists continue to create safe havens for terrorists and hinder anti-terror actions.