美国对俄罗斯实施新制裁

Washington is slapping tougher economic sanctions on Russia.

US President Barack Obama says the new sanctions target Russia's financial, energy and defence sectors.

White House spokesperson Josh Earnest says they expect the new sanctions will increase Moscow's political isolation cost to the economy.

"The United States has previously imposed sanctions on some Russian officials. And we do intend, in concert, in coordination with our European allies, to take additional steps, to impose additional economic costs, and further isolate Russia for their actions in Ukraine."

But at the same time, the White House says if Russia follows through with its commitments to help end the unrest in Ukraine, the sanctions can be rolled back.

The US penalties are paired with a new round of European Union sanctions introduced this week.

The US and the EU will both disclose the full details of their sanctions later on this Friday.

The sanctions come despite a cease-fire reached last week between Ukrainian authorities and the rebels.