US President-elect Donald Trump has praised Vladimir Putin for not expelling American diplomats, despite a similar move by Washington in response to alleged election interference.
Mr Trump tweeted: “Great move on delay – I always knew he was very smart!”
Moscow denies any involvement in election-related hacking.
But in one of the last moves of the Obama presidency, Washington demanded Russian 35 diplomats leave the country by Sunday afternoon.
Mr Putin ruled out an immediate tit-for-tat response.
The row follows allegations that Russia directed hacks against the Democratic Party and Hillary Clinton’s presidential campaign, releasing embarrassing information through Wikileaks and other outlets to help Mr Trump win the election.
Several US agencies including the FBI and the CIA say this is the case, but Mr Trump initially dismissed the claims as “ridiculous”. He has since said he will meet US intelligence chiefs to be “updated on the facts of this situation”.
The Obama administration announced retaliatory measures on Thursday:
•Thirty-five diplomats from Russia’s Washington embassy and its consulate in San Francisco were declared “persona non grata” and given 72 hours to leave the US with their families
•Two properties said to have been used by Russian intelligence services in New York and Maryland were closed on Friday
•Sanctions were announced against nine entities and individuals including two Russian intelligence agencies, the GRU and the FSB
After the US announced it would expel diplomats, Russia’s spokesman, Dmitry Peskov, had vowed Russia would respond to the “manifestation of unpredictable and aggressive foreign policy”. But he hinted it might delay its action until Mr Trump became president.
Russia’s foreign ministry suggested expelling 31 US diplomats from Moscow and four from St Petersburg.
But Mr Putin said his country would not stoop to “irresponsible diplomacy”, and invited the children of US diplomats there to spend New Year’s Eve at the Kremlin.
In a statement on the Kremlin website (in Russian), the Russian president wished President Barack Obama and his family a happy New Year, as well as Mr Trump and “the whole American people”.
The contrast between the words of the president and those of the president-elect could not be more stark.
Siding with a foreign adversary instead of the sitting president is a dramatic departure from normal diplomatic practice during this transition phase.
And Donald Trump may find himself alone in his admiration. President Obama has broad bipartisan support for his actions and a full hearing to discuss the hacking allegations has been scheduled in Congress next week.
There has been no response yet to Mr Putin’s move from the Obama administration.
However, Senator John McCain, chairman of the Senate Armed Services Committee, described the Russian hacking as an “act of war”.
“And so we have to make sure that there is a price to pay, so that we can perhaps persuade the Russians to stop these kind of attacks on our very fundamentals of democracy.”
He said a lot more needed to be done in response to the hacking, with many sanctions possible.