Cases of homegrown extremism have increased over the past month, posing a mounting threat to United States security, according to a new House Homeland Security Committee report released Monday.

The United States has recorded 39 homegrown jihadist cases across 20 states over the past 12 months, marking an 8 percent increase from March, the committee found in its monthly Terror Threat Snapshot, citing data compiled by the Majority Staff of the Homeland Security Committee.

The trend has grown drastically in the last year. More than 20 percent of the 209 homegrown extremist cases in the United States since the Sept. 11 terrorist attacks have occurred over the past 12 months, the committee reported. More than 60 percent of those cases involved arrests related to the Islamic State terrorist group.

Three Americans with suspected ties to ISIS were indicted in April on terrorism charges. Ohio resident Laith Waleed Alebbini was arrested by FBI agents on April 26 at the Cincinnati International Airport during an attempt to travel to Syria to join ISIS.

Two weeks earlier, two Illinois residents were charged with conspiring and attempting to supply material support for ISIS. Joseph Jones, also known as Yusuf Abdulhaqq, and Edward Schimenti, also known as Abdul Wali, pledged allegiance to ISIS and used social media to advocate for violent extremism on behalf of the terrorist group.

Rep. Mike McCaul (R., Texas), who chairs the Homeland Security Committee, said in a statement Monday there is a "noticeable shift" in ISIS's strategy as the U.S.-led coalition continues to weaken its territorial strongholds in Iraq and Syria.

"With the so-called ISIS ‘caliphate' in the Middle East deteriorating, jihadists are increasingly told to stay where they are and carry out attacks at home," McCaul said.

He cited the fatal shooting of a police officer claimed by ISIS last month in the heart of Paris ahead of the French presidential elections as an example of the jihadist group's "attempts to instill fear and disrupt Western life."

U.S. officials have warned that ISIS will escalate attacks against the West amid continued territorial loss.

Earlier this year, U.S. defense officials estimated that 1,900 of the roughly 7,000 foreign fighters who left the West to fight for ISIS already have filtered back into Europe. That number is expected to climb amid the U.S.-led offensive to retake Raqqa, the de facto capital of ISIS in northern Syria.