US President Donald Trump was warned in briefing materials to refrain from congratulating Russian President Vladimir Putin on his re-election but he did so anyway, a senior administration official has said.
Aides included a section in Mr Trump's briefing materials for the Tuesday morning call stating: "DO NOT CONGRATULATE," the official told the Associated Press (AP).
The White House said in a statement it is a "fireable offence and likely illegal" to leak Mr Trump's briefing papers to the press.
The message was first reported by The Washington Post.
It was unclear whether Mr Trump, who prefers oral briefings, read the talking points prepared by his national security team before the call.
National security adviser HR McMaster briefed the president in person before the call in the White House residence.
Mr Trump's call of congratulations drew him bruising criticism from members of his own party even before the Post reported that aides had given him instructions not to do so.
The president also said he and Mr Putin might meet "in the not too distant future" to discuss the arms race and other matters.
What they did not discuss on Tuesday was noteworthy as well: Mr Trump did not raise Russia's meddling in the US elections or its suspected involvement in the recent poisoning of a former spy in Britain.
"An American president does not lead the free world by congratulating dictators on winning sham elections," said Senator John McCain, who chairs the Senate Armed Services Committee and has pressed the Trump administration to respond aggressively to Russia's interference in the US presidential election.
Republican Senator Jeff Flake, a frequent Trump critic, called the president's call "odd".
Senate Majority Leader Mitch McConnell said Mr Trump "can call whomever he chooses" but noted that calling Mr Putin "wouldn't have been high on my list".
At the State Department, spokeswoman Heather Nauert said it was "no surprise" that Mr Putin was re-elected, commenting that some people were paid to turn out to vote and opposition leaders were intimidated or jailed.
She also cited a preliminary report by the Organisation for Security and Co-operation in Europe that said Russia's election took place in an overly controlled environment that lacked an even playing field for all contenders.
Her comments were notably tougher on Russia than those coming from the White House.
White House press secretary Sarah Huckabee Sanders defended Mr Trump's call and noted that former president Barack Obama made a similar call at the time of Mr Putin's last electoral victory.
"We don't get to dictate how other countries operate," Ms Sanders said.
The action and reaction fit a Trump White House pattern of declining to chide authoritarian regimes for undemocratic practices.
Mr Trump himself has long been reluctant to publicly criticise Mr Putin.
He said that during their hoped for meeting the two men would probably discuss Ukraine, Syria and North Korea, among other things.
"I suspect that we'll probably be meeting in the not too distant future to discuss the arms race, to discuss the arms race, which is getting out of control, but we will never allow anybody to have anything even close to what we have," Mr Trump said.
The briefing document with guidance for the Putin phone call is accessible only to a select group of aides, and the White House expressed anger on Wednesday that it was leaked to the media.
"If this story is accurate, that means someone leaked the President's briefing papers. Leaking such information is a fireable offense and likely illegal," the White House said in an official statement.
It was an unusual threat. Other revelations of classified material - including partial transcripts of Mr Trump's calls with foreign leaders - have not garnered specific threats of termination or criminal action.
Senator Marco Rubio called the leak a "bigger outrage" than Mr Trump's congratulations for Mr Putin.
"If you don't like President resign, but this ongoing pattern of duplicity holds potential for serious damage to the nation," he said on Twitter.
Russia has received global condemnation after Britain blamed Moscow for the recent nerve agent attack on Sergei Skripal and his daughter. Russia has denied the accusation.
Mr Trump's call came at a period of heightened tensions between the two nations after the White House imposed sanctions on Russia for its interference in the 2016 US election and other "malicious cyber attacks".
Ms Sanders insisted that the administration has scolded Mr Putin at the appropriate times.
"We've been very clear in the actions that we've taken that we're going to be tough on Russia, particularly when it comes to areas that we feel where they've stepped out of place."
The Kremlin said in a statement that Mr Trump and Mr Putin spoke about a need to "co-ordinate efforts to limit the arms race" and for closer co-operation on strategic stability and counter-terrorism.
"Special attention was given to considering the issue of a possible bilateral summit," the Kremlin statement said.
In addition, the two presidents expressed satisfaction with the apparent easing of tensions over North Korea's weapons programme, according to the Kremlin.
No details were released about the timing or location of a possible meeting, which would be their third since Mr Trump took office in January 2017.
They met on the sidelines of an international summit in Germany last summer and again more informally at another gathering of world leaders in Vietnam in November.
The presidents "agreed to develop further bilateral contacts, taking into account changes in the US State Department", the Kremlin statement said in a reference to Mr Trump's decision to replace secretary of state Rex Tillerson with CIA director Mike Pompeo.
Russia has repeatedly said it hoped for better ties with the US under Mr Trump.
Mr Putin received calls from a number of other foreign leaders, including French President Emmanuel Macron, Chinese President Xi Jinping, Japanese Prime Minister Shinzo Abe and Indian Prime Minister Narendra Modi.
Many others, including German Chancellor Angela Merkel, sent congratulatory telegrams.
The White House had said on Monday that it was "not surprised by the outcome" of Sunday's presidential election in Russia and that no congratulatory call was planned.
Mr Trump continues to grapple with the shadow of the ongoing investigation into whether his campaign colluded with Russian officials during the 2016 election that sent him to the White House.
Last month, special counsel Robert Mueller indicted 13 Russian individuals and three organisations on charges of interfering in the election.
Three of Mr Trump's associates - former national security adviser Michael Flynn, deputy campaign chairman Rick Gates and campaign aide George Papadopoulos - have pleaded guilty to lying to investigators and agreed to co-operate.
Mr Trump's former campaign chairman Paul Manafort has pleaded not guilty to a variety of money laundering and other criminal charges.