The Syrian Observatory for Human Rights said after the death of a militant commander named Abu Hayjaa al-Tunisi, who was reported to have been killed in a coalition strike on March 30, ISIS rounded up suspects from within its ranks.
"There were executions carried out by ISIS against its own people, accusing people of contacting the international coalition," said Rami Abdurrahman, head of the London-based group. "Those executions were carried out in April, and also May, in regard to the assassination of Abu Hayjaa al-Tunisi."
Abdurrahman said some ISIS fighters gave information to coalition forces because they needed money.
ISIS has lost significant revenue in recent months due to the targeting of its oil fields, and the group has reduced the salaries of some fighters, Abdurrahman said.
"Islamic State does not fully trust its leaders," he said. "There could be cells within the Islamic State organization which belong to an international intelligence agency."
ISIS' recent loss of territory in Iraq and Syria, and the deaths of several top leaders of the terror group, have fueled internal paranoia, according to analysts and U.S. officials.
One U.S. official told CNN: "ISIL is both a paranoid and death-obsessed organization. That it would execute large numbers of people, based on its paranoia, is in keeping with its inherent nature."
Michael Weiss, a CNN contributor and co-author of the book "ISIS: Inside the Army of Terror," said: "In the last several months, they lost their war minister, the number two in the organization, their so-called oil minister.
"And that has got to drive a sense of paranoia; how is the coalition able to target and successfully kill all of these ISIS operatives?
"And based on interviews I've conducted with people who defected from the group, there is a complete and total sense of paranoia — that they are being spied upon by the Bashar al-Assad regime in Syria, Iraqi intelligence in Iraq, the Kurds in northern Iraq, and indeed agents from the Russian federation or one of the coalition countries, France, Britain, the U.S."
Recent ISIS propaganda videos, translated by the SITE Intelligence Group, illustrate ISIS' apparent internal strife, and the message the terror group wants to send to potential spies.
One video shows accused spies being tied to a cross in the ISIS stronghold of Raqqa, Syria, then shot in public. Another video includes confessions of supposed spies, claiming handlers paid them for targeting information to pass to coalition forces.
The men are then strapped inside a car, which is detonated.
Last month, an ISIS propaganda magazine said a Russian female infiltrator helped kill several ISIS fighters before she was caught and executed.
"This ultraviolence that the Islamic State is increasing now, employing against its own, is meant to instill fear," said Matthew Levitt, director of the Stein Program on Counterterrorism and Intelligence at the Washington Institute for Near East Policy. "It's meant to create a disincentive that no matter how bad it gets, you don't want to cross the Islamic State."