Barack Obama also said he had signed an order enabling the US to impose sanctions on sectors of the Russian economy.
Meanwhile EU leaders have arrived in Brussels amid warnings that they may impose tougher economic sanctions.
Tensions are high as Moscow approves a treaty enabling Crimea – an autonomous republic in Ukraine – to join Russia.
Barack Obama said: “Russia must know that further escalation will only isolate it further from the international community.”
The president said the US was watching with concern the situation in southern and eastern Ukraine.
A White House official said the latest wave of US sanctions targeted 20 Russian individuals with interests in the Crimea.
Bank Rossiya is being targeted for supporting Russian government officials, the US Treasury said.
ZcOdFar5flgImage source: Wikimedia Commons President-elect Donald Trump celebrated his election victory at the Ultimate Fighting…
Millions of voters across the US chose to return Donald Trump to the White House…
Donald Trump declares victory in the US election as he addresses jubilant supporters in Florida.…
Stocks around the world are rising as Donald Trump appears to be on the cusp…
Donald Trump has won Pennsylvania, North Carolina and Georgia and taken a lead over Kamala…
Quincy Jones, the celebrated musician and producer who worked with Michael Jackson, Frank Sinatra, Ray…