The majority of the U.S. military’s support could end on Jan. 5.

In a surprising move, the Pentagon has told the Central Intelligence Agency that it plans to end the majority of the military support it provides to the agency’s counterterrorism missions by Jan. 5, according to a former senior administration intelligence official.

It is unclear how the decision would impact the spy agency’s worldwide counterterrorism missions that often rely on the U.S. military for logistical support and personnel.

Acting Defense Secretary Christopher Miller sent a letter to CIA Director Gina Haspel outlining the decision, according to the former official, who characterized the action as both surprising and unprecedented.

The CIA’s Special Activities Center carries out covert operations and has its own paramilitary force that carries out counterterrorism operations. While they act as an independent force, they often rely on the military for transportation and logistical support.

Sometimes that means that military personnel end up being detailed to support the CIA’s counterterrorism operations.

Neither the CIA nor the Defense Department responded immediately to ABC News’ requests for comment about the Pentagon’s decision.

Defense One was first to report that the Pentagon was reviewing its support to the CIA.

The online defense news outlet cited multiple officials as saying the intent behind the move is to see if Defense Department personnel “detailed” to the CIA should be diverted from counterterrorism missions and toward missions related to competition with Russia and China. Multiple former and current administration and military officials confirmed this to ABC News.

That diversion from counterterrorism missions would be in line with the National Defense Strategy that pushes the military’s focus away from the regional wars in the Middle East towards near-peer competitors like Russia and China.

“If these stories are true, they mark the end of a very strong and effective relationship between the CIA and the Defense Department,” said Mick Mulroy, a former deputy assistant secretary of defense, retired CIA paramilitary officer and ABC News contributor. “A relationship that has resulted in countless successes in the last 20 years, especially in the area of counterterrorism such as the Bin Laden and al-Baghdadi operations, but also in many that will remain unknown.”

“This could increase the risk to CIA officers until it can be readdressed by the incoming administration,” he added. “If it is not reversed, the CIA needs to be increased in personnel and funding to make up for the difference to continue their critical missions.”

Last week, a CIA paramilitary officer was killed in Somalia, according to Gen. Mark Milley, the chairman of the Joint Chiefs of Staff, who disclosed in remarks to a think tank that the deceased CIA officer had previously served in the military as a Navy SEAL.

The Pentagon announced last week that President Donald Trump had ordered the withdrawal of most of the 700 U.S. military personnel in Somalia, though it said it would continue to carry out counterterrorism missions against al-Shabab, the al-Qaida affiliate.

Presumably, the removal of most of those troops would already have had an impact on the CIA’s counterterrorism operations in that country.