WASHINGTON — U.S. officials are tracking large groups of Haitians in Latin America, including more than 20,000 in Colombia, who like the thousands now massed on the Texas border may soon try to reach the U.S., according to an internal document obtained by NBC News.

The Department of Homeland Security document also said the DHS Office of Professional Responsibility, the agency’s internal watchdog, is investigating an incident in which a Border Patrol agent on horseback in Del Rio, Texas, grabbed a Haitian migrant by the shirt. The incident, captured by a news photographer, drew widespread criticism Monday, prompting White House press secretary Jen Psaki to describe it as “horrific.”

In addition to the 20,000 Haitians gathered in northern Colombia, DHS is also monitoring groups of about 1,500 in Panama and 3,000 in Peru, the document said. A senior DHS official said it remains to be seen when and whether those migrants will come to the U.S., but they have begun “staging” in the various countries, potentially signaling they are planning to travel in large numbers.

Like the surge of 15,000 Haitian migrants who arrived in Del Rio over the past week, most of the migrants in Central and South America left Haiti years ago, many of them after the 2010 earthquake, and have been living in other countries.

Recent economic conditions in those countries, as well as what Homeland Security Secretary Alejandro Mayorkas described as misinformation about the Biden administration’s willingness to take in Haitians, have triggered many to seek protections in the U.S.

When DHS has previously monitored caravans of migrants headed to the U.S. border in large numbers, there has been a two to three-week lag between their departure and their arrival. But many of the recently arrived Haitians took buses through Mexico, expediting their arrival and increasing their numbers.

A CIA official reported symptoms consistent with so-called Havana Syndrome, a mysterious affliction that has struck diplomats, spies and other government workers at home and abroad, two sources familiar with the matter told NBC News on Monday.

The unidentified employee was traveling with CIA director Bill Burns during a trip to India this month. The employee was immediately tested as part of a protocol the CIA has established to deal with the mysterious brain symptoms typically associated with Havana Syndrome and is receiving medical treatment, the sources said.

The incident was first reported by CNN.

This is the latest reported case of a U.S. government employee reporting symptoms associated with the mysterious ailment. Havana Syndrome first came into public view in 2017 after U.S. diplomats and other government workers stationed in Cuba reported feeling unusual physical sensations after hearing strange high- and low-pitched sounds. U.S. government employees have also reported cases while in China and the Washington, D.C. area.

In late August, at least two U.S. diplomats were medically evacuated from Vietnam after Havana Syndrome incidents were reported in the capital city of Hanoi ahead of Vice President Kamala Harris’ arrival.

“The health and well-being of American public servants is of paramount importance to the administration, and we take extremely seriously any report by our personnel of an anomalous health incident,” a senior administration official said Monday night. “It is a top priority for the U.S. government to determine the cause of these incidents as quickly as possible and that we ensure any affected individuals get the care they need.”

Many people who have experienced Havana Syndrome report experiencing vertigo, dizziness, fatigue, nausea and intense headaches. Some describe it as being hit by an invisible blast wave. Some have no longer been able to work.

The India incident has raised questions about whether a foreign adversary had intentionally targeted the CIA director’s staff, but the sources said the agency is unclear what exactly could have caused the incident. The case is one of a number of new incidents in recent months involving CIA personnel who experienced what U.S. officials call “anomalous health incidents,” the sources said.

A CIA spokeswoman declined to confirm the case in India but said the U.S. government and the agency are taking every incident seriously.

“Director Burns has made it a top priority to ensure officers get the care they need and that we get to the bottom of this,” the spokeswoman said. “We’ve strengthened efforts to determine the origins of the incidents, including assembling a team of our very best experts — bringing an intensity and expertise to this issue akin to our efforts to find Bin Ladin.”

The spokeswoman added that a panel of experts has been convened from across intelligence agencies “to work collectively to increase our understanding of the possible mechanisms that could be causing [anomalous health incidents].”

Many U.S. officials suspect the incidents, which have caused permanent brain injuries in some victims, are a result of an attack or surveillance operation by Russian spies, but the evidence is inconclusive.

The National Academies of Sciences said in a report last year the most likely cause of the injuries was directed microwave energy, but that conclusion is being debated in the scientific community.

Last week, deputy CIA director David Cohen said the agency is getting closer to solving the mystery, but there are limitations.

“In terms of have we gotten closer, I think the answer is yes — but not close enough to make analytic judgment that people are waiting for,” he said.

Ken Dilanian

Ken Dilanian is a correspondent covering intelligence and national security for the NBC News Investigative Unit.

Dartunorro Clark

Dartunorro Clark covers politics, including the Covid-19 recovery, for NBC News.

Josh Lederman contributed.