Obama expands sanctions on Russia

US President Barack Obama has imposed sanctions on more Russian officials and a bank and threatened to target the broader Russian economy if Moscow escalates its actions against Ukraine.

"Russia must know that further escalation will only isolate it further from the international community," Obama said on Thursday at the White House.

The new measures targeted a new list of 20 MPs and senior government officials in addition to 11 people already sanctioned by Washington.

Obama made his announcement just hours after Russian MPs rubber-stamped a treaty signed by President Vladimir Putin to absorb the Ukrainian region of Crimea into Russia.

The US move freezes assets within American jurisdiction and bars US firms from conducting business with those concerned.

The US Treasury Department identified the financial institution involved as Aktsionerny Bank of the Russian Federation, also known as Bank Rossiya.

Senior officials said the bank held significant assets of the Russian ruling elite and key figures around Russian President Vladimir Putin.

"Bank Rossiya's shareholders include members of Putin's inner circle associated with the Ozero Dacha Cooperative, a housing community in which they live," the US Treasury said.

Obama said the US was taking the steps as part of a response to what Russia has already done in Crimea.

But he also raised the prospect of tougher future action if Russian behaviour does not change, adding he had signed a new executive order that would allow him to target specific sectors of the Russian economy.

"This is not our preferred outcome," Obama said, warning that the moves would have a "significant impact" on the Russian economy.