U.S. military bases and personnel across Europe are on heightened alert, after new intelligence warned of a possible terror attack targeting either facilities or personnel.

A U.S. defense official Monday confirmed to VOA that military installations across U.S. European Command (EUCOM) have been elevated to Force Protection Condition Charlie, which means an attack of some sort is likely.

The official did not elaborate on the contents of the intelligence that sparked the change, although counterterrorism officials from multiple countries have warned of an increased threat, including some surrounding the upcoming Summer Olympics in Paris.

The U.S. defense official said that the military is taking extra steps to ensure [U.S. troops] remain vigilant during both business and pleasure activities.

A second U.S. official, speaking on the condition of anonymity to discuss intelligence matters, emphasized it was the overall threat picture and not one single piece of intelligence, that led to the increased force protection posture.

There is no specific or imminent threat to U.S. forces in Europe, the official told VOA. This was a step taken out of an abundance of caution.

A statement Monday from EUCOM likewise indicated the increased security measures are the result of a combination of factors.

Our increase in vigilance is not related to any one single threat, but out of concern of a combination of factors such as ongoing and upcoming large public forums including the Euro Cup and the Olympics, along with an increasing the threat of attacks by potential bad actors against various non-military targets in Europe, the statement read.

EUCOM advises personnel in the European theater to remain vigilant and stay alert at all times, including reporting suspicious activity, monitoring Department of State travel advisories, and implementing prudent personal risk mitigation measures, it added.

A report issued last month by the by the cybersecurity firm Recorded Future warned that despite a high risk of cyberattacks, the greatest threat to the Paris Olympics remains the possibility for terror attacks.

A French gendarme walks past the logo of the Paris 2024 Olympic and Paralympic Games in front of the National Assembly in Paris, May 2, 2024.

French authorities have already disrupted at least two separate terror plots. In one of the cases, the 18-year-old suspect was charged with plotting to carry out an attack on one of the stadiums serving as Olympic venues in the name of the Islamic State.

Top U.S. counterterrorism officials have also acknowledged that the Islamic State terror group, known as IS or ISIS, has also been gaining momentum in recent months.

Much of the concern has focused on the groups Afghan affiliate, known as IS-Khorasan.

Both ISIS and ISIS-Khorasan ¦ have demonstrated a capability and intent to conduct external operations, White House Deputy Homeland Security Advisor Jen Daskal told a counterterrorism conference in Omaha, Nebraska, last week.

National Counterterrorism Center Director Christine Abizaid also warned about IS-Khorasan this past May.

This ability of the global ISIS enterprise, even without territorial solidity, the ability to reach out virtually to a network of supporters, some of whom are going to conduct attacks, is quite concerning, she told a security conference in Doha.

Abizaid further called IS-Khorasans ability to reestablish itself in Afghanistan probably the most significant additive capability weve seen to the global ISIS network in the last three years.

IS-Khorasan claimed responsibility for the January attack on a memorial service in Kerman, Iran, that killed about 90 people, and also the March attack on a Moscow concert hall that killed more than 140 people.

U.S. counterterrorism officials have also raised concerns that IS-Khorasan has become more adept at using transnational criminal networks and human smuggling rings, eying potential plots to send its operatives into the United States. (VOA)

FILE PHOTO: The main entrance for the U.S. Army Patch Barracks in Stuttgart, Germany, Nov. 28, 2006, where the headquarters of the U.S. European Command is located. The U.S, military has raised the security protection measures it is taking at its bases throughout Europe.