A number of U.S. federal laws grant agencies the authority to investigate extraterritorial criminal and terrorist activity—and several agencies actively do so around the globe. Below are some of the key players:

FBI – Legal Attaché Offices ("Legats")

The Federal Bureau of Investigation (FBI) maintains attaché offices—commonly known as legal attachés or legats—in 23 foreign liaison posts, with sub-offices in additional key cities worldwide. These legats work closely with American embassies and local law enforcement agencies on criminal and counterterrorism cases within FBI jurisdiction. Approximately 250 special agents and support staff are stationed in these offices, conducting international investigations and providing liaison services.

Diplomatic Security Service (DSS)

The Diplomatic Security Service (DSS) operates the Overseas Criminal Investigations (OCI) program, which has the largest global investigative footprint of any U.S. federal law enforcement entity, with operations in 118 locations worldwide.

The OCI program employs around 130 Overseas Criminal Investigators (OCIs) who focus on identifying and disrupting transnational criminal networks targeting the U.S. In addition to OCIs, the DSS deploys hundreds of Regional Security Officers (RSOs), Assistant RSOs (ARSOs), Diplomatic Couriers, and Security Engineers. RSOs also oversee U.S. Marine Security Guards assigned to embassies.

Homeland Security Investigations (HSI)

A division of the Department of Homeland Security (DHS), Homeland Security Investigations (HSI) maintains a strong international presence, with around 500 special agents deployed across more than 80 offices in over 50 countries. HSI agents work alongside foreign and interagency partners to pursue cases involving drug trafficking, human smuggling, weapons, money laundering, and other transnational crimes. They conduct arrests, collect evidence, and lead international operations.

U.S. Marshals Service

The U.S. Marshals Service (USMS) operates a U.S.-based Office of International Operations (OIO), which oversees field offices in the Dominican Republic, Jamaica, Colombia, and Mexico. These offices support investigations on behalf of U.S. federal, state, and local agencies, as well as international law enforcement authorities.

U.S. Marshals collaborate closely with the DSS, Interpol, and local counterparts to track and apprehend fugitives who have fled abroad.

Other Federal Agencies with International Operations

Several additional agencies maintain attachés or foreign divisions, including:

• Drug Enforcement Administration (DEA)
• Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF)
• Central Intelligence Agency (CIA)
• Defense Intelligence Agency (DIA)

To a lesser extent, military-affiliated investigative bodies also operate internationally, particularly on or near U.S. military bases. These include:

• Defense Criminal Investigative Service (DCIS) – part of the Department of Defense
• Naval Criminal Investigative Service (NCIS)
• Air Force Office of Special Investigations (OSI)
• U.S. Army CID and Marine Corps CID

These agencies conduct investigations related to national security, military jurisdiction, and criminal offenses involving U.S. service members abroad.

Jurisdiction and Use of Force Abroad

While U.S. agents operating overseas conduct investigations and gather intelligence, they generally cannot make arrests on foreign soil. Instead, they rely on local law enforcement to carry out arrests. In practice, the level of cooperation depends on the host country’s laws, diplomatic ties, and the nature of the case. In many instances, strong U.S. influence can expedite action by local authorities—especially in high-profile or transnational cases.

Some agents do operate armed, depending on country-specific agreements. For example, in Mexico, the U.S. Embassy has secured a private security firearms license, allowing certain personnel to carry weapons legally. Mexican law also permits foreign dignitaries and their protection teams to carry firearms under strict conditions and prior approval.