Lawyers for former national security adviser Michael Flynn have told US President Donald Trump's legal team that they are no longer communicating with them about special counsel Robert Mueller's investigation into Russian election interference.
Mr Flynn's legal team communicated the decision this week. The New York Times first reported the decision.
The decision could be a sign that Mr Flynn is moving to co-operate with Mr Mueller's investigation or negotiate a deal for himself.
In large criminal investigations, defence lawyers routinely share information with each other. But it can become unethical to continue such communication if one of the potential targets is looking to negotiate a deal with prosecutors.
Robert Kelner, a lawyer for Mr Flynn, declined to comment, as did a lawyer for Mr Flynn's son, Michael Flynn Jr, who has also come under investigation from Mr Mueller's prosecutors.
Mr Flynn was forced to resign as national security adviser in February after White House officials concluded that he had misled them about the nature of his contacts during the transition period with the Russian ambassador to the United States.
He was interviewed by the FBI in January about his communications with the ambassador, Sergey Kislyak. The deputy attorney general at the time, Sally Yates, soon advised White House officials that their public assertions that Mr Flynn had not discussed sanctions with Mr Kislyak were incorrect and that Mr Flynn was therefore in a compromised position.
Mr Flynn was facing a Justice Department investigation over his foreign business dealings even before Mr Mueller was appointed as special counsel in May to investigate potential co-ordination between the Trump campaign and Russia to influence the 2016 presidential election. Mr Mueller has since inherited that investigation.
Mr Flynn, a prominent Trump backer in the campaign, has been a key figure in Mr Mueller's probe and of particular interest to Mr Trump.
Former FBI director James Comey, for instance, said that Mr Trump encouraged him to end an FBI investigation into Mr Flynn during a private Oval Office meeting in February.
In addition to scrutinising Mr Flynn's contacts with Russia during the transition and campaign, Mr Mueller has been investigating the retired US Army lieutenant general's role in $530,000 worth of lobbying work his now-defunct firm performed for a Turkish businessman during the final months of the 2016 presidential campaign.
The lobbying campaign sought to gather derogatory information on Fethullah Gulen, a Turkish cleric and green-card holder living in Pennsylvania.
Turkish President Recep Tayyip Erdogan has accused Mr Gulen of being behind a botched coup and has sought his extradition. Mr Gulen has denied the allegations, and US officials have rebuffed Turkey's extradition demands, citing a lack of evidence.
Mr Flynn and his firm, Flynn Intel Group, carried out the lobbying and research work for several months, meeting with officials from the US and Turkish governments.
Mr Flynn also published an op-ed on Election Day in The Hill newspaper, parroting many of the Turkish government's talking points about Mr Gulen. At the time, neither Mr Flynn nor his company was registered with the Justice Department to represent Turkish interests.
Soon after the publication of the op-ed, the Justice Department began investigating Mr Flynn's lobbying work, and in March, he registered with the department as a foreign agent. In federal filings, Mr Flynn acknowledged the work could have benefited the government of Turkey.
Since then, FBI agents working for Mr Mueller have been investigating whether the Turkish government was directing the lobbying work and not a private company owned by a Turkish businessman, Ekim Alptekin, as Mr Flynn's firm has contended.
FBI agents have also been asking about Mr Flynn's business partner, Bijan Kian, who served on Mr Trump's presidential transition, and Mr Flynn's son, who worked for his father as part of the lobbying campaign.
Mr Flynn Jr was also a near constant presence around his father during the Trump campaign and presidential transition period.
Mr Mueller announced his first charges in the investigation last month, including the guilty plea of a foreign-policy adviser to the campaign, George Papadopoulos, and the indictments of former campaign chairman Paul Manafort and business associate Rick Gates.