Under siege in Iraq and Syria, the Islamic State group is lashing out with an unprecedented display of violence as its leaders work to close ranks and keep supporters' interest. Militants with the group also known as ISIS have beheaded family members, drowned dissenters and bombed Muslims gathered for prayers in recent days as U.S.-led forces launched a campaign to take back Mosul, Iraq’s second largest city.

Last week, one ISIS supporter in Mosul reportedly beheaded his father for insulting the terrorist group’s leader, Abu Bakr al-Baghdadi. In Baghdad, ISIS supporters carried out a bombing attack Saturday that killed 41 people at a Shiite Muslim gathering. ISIS militants also executed 57 supporters for treason in Mosul, the group's last stronghold in Iraq, drowning their bodies and dumping them in a mass grave, Reuters reported Friday. 

“Those were Daesh members who turned against the group in Mosul," Iraqi Counterterrorism Service spokesman Sabah al-Numani in Baghdad told Reuters, using an Arabic acronym for ISIS. "This is a clear sign that the terrorist organization has started to lose support not only from the population, but even from its own members.”

In all, attacks carried out by ISIS in Iraq and Syria were up by 17 percent as of May compared with last year, according to the global analysis firm IHS Jane's Terrorism and Insurgency Centre. The 891 attacks resulting in 2,150 non-militant deaths marked the highest record violence since ISIS seized the Iraqi city of Mosul in 2014. 

"Following territorial losses, we are seeing a steady upward trend in the tempo of Islamic State operations worldwide, but particularly in Syria and Iraq," said Matthew Henman, head of IHS Jane's Terrorism and Insurgency Centre in a statement. "Attack and fatality numbers have jumped. The group is resorting more and more to mass-casualty violence as it comes under heavy pressure from multiple angles."

More than 40,000 Iraqi and Kurd troops are leading the fight to win Mosul from ISIS, along with air and ground support from 60 nations led by the U.S. ISIS is considered to be greatly outnumbered, with only 5,000 Islamic State fighters in Mosul.