Two senior ISIS leaders were arrested on Monday while trying to cross the border from Syria, Iraq's security forces said. One of the men was in charge of the group's Zakat Fund in the cities of Tell Afar and Hadhar outside the city of Mosul in northern Iraq, the Iraqi military said. The men had been tracked by the Intelligence Service of the Iraqi Army 15th Division. Zakat is one of Islam’s five pillars. Muslims with sufficient income are required to pay a certain amount each year and Zakat contributions are supposed to help the poor. But in typical fashion, ISIS twisted this religious tradition and instead used donations to finance its operations. The second militant was in charge of ISIS' "War Spoils Diwan", said the military. That department was in charge of counting and safekeeping material, both civilian and military, captured during ISIS operations. Both men were active at the time when ISIS overran large areas in northern and western Iraq following its 2014 blitz, which ended up with the group declaring an Islamic “caliphate” in vast parts of Iraq and Syria, totaling around one third of Iraq at one point. The military did not reveal the names or nationalities of the arrested pair. Requests to security officials for more details went unanswered. ISIS was briefly the richest terrorist organisation in the world, before a major international counter-terrorism effort slowly cut off their foreign donations. Oil infrastructure which they had captured from the Syrian government was also bombed, depriving them of yet more revenue. Backed by US-led International Coalition, Iraqis declared ISIS defeated in late 2017 after driving the militants from all areas that they occupied. But despite continuous operations by Iraqi Security Forces that killed and arrested thousands of the militants, the group is still posing a challenge, planning and carrying out attacks mainly in remote rural areas. This month, Kurdish authorities foiled an ISIS plot to attack the city of Erbil, the capital of the self-ruled Iraqi Kurdistan region. The region’s Prime Minister, Masrour Barzani, said the plot originated in Al Hol internment camp in neighbouring Syria where thousands of Syrian and foreign nationals with links to ISIS are held. The five-member cell was arrested in Erbil. They were smuggled out of Syria before reaching Iraqi Kurdistan through Turkey and Iran.