Retired Lt. Gen. Mike Flynn, former national security adviser to President Trump, is likely bound by an administration ethics rule that prevents him lobbying for five years and never again lobbying for a foreign government, White House press secretary Sean Spicer said Monday.

"That would be correct," Spicer said when asked if the president's lobbying ban would apply to Flynn, who stepped down last month.

"I'd have to check and actually figure out when he signed or if he signed the form," Spicer added. "But yes, all administration officials who come in are required to sign that ethics pledge banning them from lobbying for five years and then a lifetime ban on lobbying on behalf of any foreign government."

Trump asked Flynn for his resignation in February amid reports that Flynn had discussed sanctions with the Russian ambassador prior to the inauguration before telling Vice President Mike Pence and other senior administration officials that the issue of sanctions hadn't come up. When leaked transcripts later demonstrated that Flynn and the Russian ambassador had indeed discussed sanctions, Flynn told reporters he did not recall the details of the conversation.

Flynn's recent registration with the Justice Department as a foreign lobbyist has raised fresh questions about whether Trump's former national security adviser had a conflict of interest when he took a position in the White House.

Spicer said last week that while the transition team had been made aware of the Justice Department's recommendation to Flynn that he should register his foreign lobbying activity before Inauguration Day, the transition's lawyer considered Flynn's registration status a private matter for his personal attorneys to handle.

The White House has said Trump was not aware of Flynn's advocacy for Turkish interests when offering Flynn a high-profile national security position.

Spicer said Monday he was unsure of the enforcement mechanism associated with Trump's lobbying ban. As part of his campaign pledge to "drain the swamp," Trump banned his administration staff from registering as domestic lobbyists for five years after their departure from government and prevented them from registering as foreign lobbyists for life.

"I don't know whether that's a Department of Justice aspect or not," Spicer said of how the lobbying ban would be enforced.