Originally Published: 21 JUL 22 10:20 ET

Updated: 21 JUL 22 10:34 ET

By Whitney Wild and Jeremy Herb, CNN

(CNN) -- The Department of Homeland Security inspector general has directed the Secret Service to stop its internal investigations into what happened to text messages related to January 6 that may have been deleted, according to a letter reviewed by CNN.

The inspector general wrote that the Secret Service should stop investigating the matter because it could interfere with the inspector general's own investigation into what happened to the agency's text messages.

The letter adds to the growing tension between the Secret Service and the DHS inspector general over the potentially missing text messages, which are being sought by the House select committee as part of its investigation into former President Donald Trump's actions and movements on January 6, 2021.

"To ensure the integrity of our investigation, the USSS must not engage in any further investigative activities regarding the collection and preservation of the evidence referenced above," DHS deputy inspector general Gladys Ayala wrote in a letter to Secret Service Director James Murray on Wednesday evening. "This includes immediately refraining from interviewing potential witnesses, collecting devices or taking any other action that would interfere with an ongoing criminal investigation."

The inspector general wrote that the Secret Service should explain what interviews had already been conducted related to the text messages, along with the "scope off the questioning, and what, if any, warnings were given to the witness(es)." The inspector general told the Secret Service to respond by Monday.

The new letter comes after the Secret Service was only able to provide a single text message to the inspector general, who had requested a month's worth of records for 24 Secret Service personnel, according to a letter to the select committee.

CNN has reached out for comment to the Secret Service and the DHS inspector general.

The directive could complicate the Secret Service's response to a subpoena it received from the House select committee last week, as well as a request from the National Archives this week to the DHS records officer asking the agency to clear up if the text messages were deleted and explain why.

The select committee's chairman, Democratic Rep. Bennie Thompson of Mississippi, wrote in a letter to the Secret Service director that the panel was seeking text messages from January 5-6, 2021.

In a joint statement Wednesday, Thompson and committee vice chair Rep. Liz Cheney said they "have concerns" about how the Secret Service cell phone data was deleted.

"The procedure for preserving content prior to this purge appears to have been contrary to federal records retention requirements and may represent a possible violation of the Federal Records Act," they said.

The Secret Service told the committee this week that it was engaged in "extensive efforts" to determine whether any text messages had been lost and if they were recoverable. Those steps included "the pulling of any available metadata to determine what, if any, texts were sent or received on the devices of the identified individuals," the agency said in a letter, as well as interviewing the 24 individuals "to determine if messages were stored in locations that were not already searched by the Secret Service."

The inspector general has alleged that the Secret Service erased text messages from January 5 and 6, 2021, not long after they had been requested by oversight officials investigating the Secret Service's response to the January 6 attack on the Capitol, according to a letter that the inspector general sent to the House select committee.

The Secret Service has previously explained that it was up to employees to conduct the necessary preservation of records from their phones. The letter said the service did provide personnel a "step-by-step" guide to preserve mobile phone content, including text messages, prior to the phone migration that began January 27, 2021. It went on to explain that "all Secret Service employees are responsible for appropriately preserving government records that may be created via text messaging."