The Department of Homeland Security warned of an increased threat of domestic terror for the spring and summer Friday as expiring coronavirus restrictions are expected to lead to larger public gatherings, which make appealing soft targets for attackers.

"Violent extremists may seek to exploit the easing of COVID-19-related restrictions across the United States to conduct attacks against a broader range of targets after previous public capacity limits reduced opportunities for lethal attacks," the DHS said in National Terrorism Advisory System Bulletin.

Homeland Security Secretary Alejandro Mayorkas looks on during a break in a Senate Appropriations committee hearing to examine domestic extremism, Wednesday, May 12, 2021 on Capitol Hill in Washington. (Alex Wong/Pool via AP)

The Centers for Disease Control and Prevention updated its guidance earlier this week, and a number of states are easing restrictions on public spaces, businesses, schools and other community fixtures.

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Many past incidents have targeted houses of worship and commercial centers, the DHS said, warning that potential attackers could be influenced by foreign terror groups, Internet conspiracy theories and U.S. adversaries like Russia, China and Iran.

"We are advising the public to be vigilant about ongoing threats to the United States, including those posed by domestic terrorism, grievance-based violence, and those inspired or influenced by foreign terrorists and other malign foreign influences," DHS Secretary Alejandro Mayorkas said in a statement. "In this evolving threat environment, DHS is redoubling our efforts to detect and disrupt all forms of foreign and domestic terrorism and targeted violence, while safeguarding privacy protections, civil rights, and civil liberties."

The DHS notice also warned that extremists could attempt to hijack left-wing protests against police violence or racial injustice.

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"Opportunistic violent criminals are likely to exploit Constitutionally-protected freedom of speech activity linked to racial justice grievances and police use of force concerns, potentially targeting protestors perceived to be ideological opponents," the notice reads.

Authorities are urging Americans who witness suspicious activity or threats of violence to report them to local law enforcement or the FBI.