People flee the scene of a terror attack at Istanbul's Ataturk airport on June 29. Turkish officials have strong evidence that ISIS leadership was involved in the planning of the attack, a senior government source told CNN. Officials believe the men -- identified by state media as being from Russia, Uzbekistan and Kyrgyzstan -- entered Turkey from the ISIS stronghold of Raqqa in Syria, bringing with them the suicide vests and bombs used in the attack, the source said.
Defne Karadeniz/Getty Images
The ISIS militant group -- led by Abu Bakr al-Baghdadi, pictured -- began as a splinter group of al Qaeda. Its aim is to create an Islamic state, or caliphate, across Iraq and Syria. It is implementing Sharia law, rooted in eighth-century Islam, to establish a society that mirrors the region's ancient past. It is known for killing dozens of people at a time and carrying out public executions.
Al-Furqan Media/Anadolu Agency/Getty Images
Kurdish Peshmerga fighters fire missiles during clashes with ISIS in Jalawla, Iraq, on June 14, 2014. That month, ISIS took control of Mosul and Tikrit, two major cities in northern Iraq.
RICK FINDLER/AFP/Getty Images
Traffic from Mosul lines up at a checkpoint in Kalak, Iraq, on June 14, 2014. Thousands of people fled Mosul after it was overrun by ISIS.
Dan Kitwood/Getty Images
ISIS fighters parade down an Iraqi street in this image released by the group in July 2014.
Aziza Hamid, a 15-year-old Iraqi girl, cries for her father while she and other Yazidi people are flown to safety after a dramatic rescue operation at Iraq's Mount Sinjar on August 11, 2014. A CNN crew was on the flight, which took diapers, milk, water and food to the site where as many as 70,000 people were trapped by ISIS. Only a few of them were able to fly back on the helicopter with the Iraqi Air Force and Kurdish Peshmerga fighters.
On August 19, 2014, American journalist James Foley was decapitated by ISIS militants in a video posted on YouTube. A month later, they released videos showing the executions of American journalist Steven Sotloff and British aid worker David Haines.
NICOLE TUNG/AFP/Getty Images
ISIS militants stand near the site of an airstrike near the Turkey-Syria border on October 23, 2014. The United States and several Arab nations began bombing ISIS targets in Syria to take out the group's ability to command, train and resupply its fighters.
BULENT KILIC/AFP/Getty Images
A Kurdish marksman stands atop a building as he looks at the destroyed Syrian town of Kobani on January 30, 2015. After four months of fighting, Peshmerga forces liberated the city from the grip of ISIS.
BULENT KILIC/AFP/Getty Images
Safi al-Kasasbeh, right, receives condolences from tribal leaders at his home village near Karak, Jordan, on February 4, 2015. Al-Kasasbeh's son, Jordanian pilot Moath al-Kasasbeh, was burned alive in a video that was released by ISIS militants. Jordan is one of a handful of Middle Eastern nations taking part in the U.S.-led military coalition against ISIS.
In February 2015, British newspapers report the identity of "Jihadi John," the disguised man with a British accent who had appeared in ISIS videos executing Western hostages. The militant was identified as Mohammed Emwazi, a Kuwaiti-born Londoner. On November 12, 2015, the Pentagon announced that Emwazi was in a vehicle hit by a drone strike. ISIS later confirmed his death.
DANIEL SORABJI/AFP/Getty Images
In March 2015, ISIS released video and images of a man being thrown off a rooftop in Raqqa, Syria. In the last photograph, the man is seen face down, surrounded by a small crowd of men carrying weapons and rocks. The caption reads "stoned to death." The victim was brutally killed because he was accused of being gay.
An Iraqi soldier searches for ISIS fighters in Tikrit on March 30, 2015. Iraqi forces retook the city after it had been in ISIS control since June 2014.
Dead bodies lie near a beachside hotel in Sousse, Tunisia, after a gunman opened fire on June 26, 2015. ISIS claimed responsibility for the attack, which killed at least 38 people and wounded at least 36 others, many of them Western tourists. Two U.S. officials said they believed the attack might have been inspired by ISIS but not directed by it.
Jawhara FM via AP
ISIS also claimed responsibility for what it called a suicide bombing at the Al-Sadiq mosque in Kuwait City on June 26, 2015. At least 27 people were killed and at least 227 were wounded, state media reported at the time. The bombing came on the same day as the attack on the Tunisian beach.
YASSER AL-ZAYYAT/AFP/Getty Images
A man inspects the aftermath of a car bombing in Khan Bani Saad, Iraq, on July 18, 2015. A suicide bomber with an ice truck, promising cheap relief from the scorching summer heat, lured more than 100 people to their deaths. ISIS claimed responsibility on Twitter.
Two women hold hands after an explosion in Suruc, Turkey, on July 20, 2015. The blast occurred at the Amara Cultural Park, where a group was calling for help to rebuild the Syrian city of Kobani, CNN Turk reported. At least 32 people were killed and at least 100 were wounded in the bombing. Turkish authorities said they believed ISIS was involved in the explosion.
DEPO PHOTOS/AFP/Getty Images
Spectators at the Stade de France in Paris run onto the soccer field after explosions were heard outside the stadium on November 13, 2015. Three teams of gun-wielding ISIS militants hit six locations around the city, killing at least 129 people and wounding hundreds.