A group of gunmen, including two suicide bombers, stormed a coffee shop where Real Madrid fans gathered in a town north of Baghdad early on Friday, killing at least 13 people and wounding 15 there, Iraqi officials said.
Real Madrid issued a statement later on Friday saying the club "deeply regret the attack.
The club will wear black armbands in their final league game of the season on Saturday against Deportivo La Coruna.
Photos from the attack's aftermath showed Real Madrid banners hanging in the cafe, and La Liga also wrote a message of support on Twitter.
#LaLiga's thoughts are with the victims & familes after hearing about the attack on a Real Madrid Peña in Iraq. pic.twitter.com/6SLY8mjVeU
- LaLiga (@LaLigaEN) May 13, 2016
The Islamic State group posted a statement online claiming responsibility for the attack, which took place shortly after midnight Thursday in Balad, 80 kilometres (50 miles) north of the Iraqi capital.
According to Iraqi officials, three gunmen armed with machine guns opened fire into the crowded Balad cafe and once police arrived at the scene, two of the attackers detonated their suicide vests.
AS reported that 50 members of a Real Madrid fan club were in the cafe at the time of the attack.
"A group of Islamic terrorists, from ISIS, came into the cafe, armed with AK-47s, shooting at random at everyone who was inside," the club's president, Ziad Subhan, told AS.
The attack comes on the heels of a two-day wave of bombings in the Iraqi capital that killed nearly 100 people.
Real Madrid's statement read: "The club mourn and offer condolences to the family and friends of the victims.
"Real Madrid extend their solidarity to the entire country of Iraq, which suffers the injustice of extreme violence."