White House national security adviser Michael Flynn privately discussed US sanctions against Russia with Moscow’s ambassador to the United States during the month before President Donald Trump took office, the Washington Post reported on Thursday.

Citing nine unnamed current and former US officials, the Post said some senior US officials interpreted the contacts as a “potentially illegal” signal to Russia that it could expect a reprieve from sanctions imposed by the Obama administration in December.

Reuters could not immediately confirm the Washington Post report.

Reuters reported last month, citing three sources familiar with the matter, that Flynn had held five phone calls with Russian ambassador Sergei Kislyak on 29 December, the day then-President Barack Obama retaliated for Moscow’s alleged interference in the 2016 US presidential election.

The Post said Flynn on Wednesday denied that he had discussed sanctions with the Russian ambassador, but on Thursday backed away from the denial through a spokesman.

Flynn “indicated that while he had no recollection of discussing sanctions, he couldn’t be certain that the topic never came up,” the Post quoted the spokesman as saying.

Officials said this week that the FBI is continuing to examine Flynn’s contacts with Kislyak, according to the paper.

“Several officials emphasised that while sanctions were discussed, they did not see evidence that Flynn had an intent to convey an explicit promise to take action after the inauguration,” the Post said.