US expels 35 Russian diplomats over alleged election hacking and harassment in Moscow
The United States has expelled 35 Russian diplomats from the country - giving them 72 hours to leave.
Two Russian compounds in New York and Maryland were also closed down in response to alleged cyber hacking of the US election and harassment of American diplomats in Moscow.
Additionally, a number of sanctions have been issued against Russian individuals deemed responsible for "undermining election processes and or institutions".
The move was described by Barack Obama as a "necessary and appropriate response" to efforts to "harm" US interests.
A presidential statement described alleged Russian hacking and harassment as "in violation of established international norms of behaviour".
In his statement, President Obama said US diplomats in Moscow had experienced unacceptable levels of harassment by Russian security services and police over the last year.
He also warned that data theft and disclosure activities could only have been directed by the highest levels of the Kremlin.
Measures being taken in response included sanctions against nine individuals and entities - among those the GRU, Russia's main foreign-intelligence service.
Compounds in Maryland and New York are to be shut down, while declassified technical information on Russian civilian and military intelligence service cyber activity will be released by the FBI.
President Obama said his actions were the "sum total of our response to Russia's aggressive activities".
"These actions follow repeated private and public warnings that we have issued to the Russian government, and are a necessary and appropriate response to efforts to harm U.S. interests in violation of established international norms of behavior," he said.
The outgoing US leader said that all Americans should be "alarmed" by Moscow's actions.
He reiterated his government's belief that Russian cyber-hackers had interfered with the US election process.
Obama also described harassment of US diplomats in Russia as "unacceptable".
"Such activities have consequences. Today, I have ordered a number of actions in response," he said.
The FSB, two Russian intelligence services, four individual offices of the GRU and three companies that provided material support for the GRU have also been hit with sanctions.
Obama warned: "We will continue to take a variety of actions at a time and place of our choosing, some of which will not be publicized.
"In addition to holding Russia accountable for what it has done, the United States and friends and allies around the world must work together to oppose Russia’s efforts to undermine established international norms of behavior, and interfere with democratic governance."
He announced that a report on Russian's alleged attempts at interfering in the election would be presented to Congress in the coming days.