The Kremlin has lashed out at the White House after it backed up an allegation from the US Treasury Department that President Vladimir Putin is corrupt.

Adam Szubin, the US Treasury acting under secretary for terrorism and financial intelligence, said in a BBC documentary that aired on Monday that Putin was a “picture of corruption”.

The White House press secretary, Josh Earnest, on Thursday backed up that line, saying that the Treasury’s assessment “best reflects the administration view”.

The Kremlin had already dismissed the US Treasury claim that it said amounted to an “official accusation” but ratcheted up the rhetoric after the White House got involved.

“We consider this statement outrageous and offensive,” spokesman Dmitry Peskov told journalists.

“We really need further explanation because such a statement is absolutely unprecedented.”

Ties between Moscow and Washington have plunged to their lowest point since the cold war over Russia’s meddling in Ukraine.

The two sides, however, are currently engaged in an international peace push on the conflict in Syria, although they support different sides in the civil war.

Peskov accused Washington of firing the starting gun on attempts to discredit Putin ahead of Russia’s next presidential election in 2018, even though he insisted Putin has not yet decided to run.

In a sign that the allegations could further damage ties between the two countries, the foreign minister, Sergei Lavrov, raised the issue with his US counterpart John Kerry, in a phone call Friday.

“Lavrov expressed outrage at the contrived and unforgivable allegations against the Russian leadership,” Russia’s foreign ministry said in a statement.

“It was emphasised that the blame for the deliberate whipping up of tension in bilateral affairs falls squarely on Washington,” the statement said.

Russian authorities have repeatedly accused the west of plotting to overthrow Putin, but critics insist an elite around the strongman is whipping up public fears as they cement their grip over the country’s vast wealth.