U.S. President Barack Obama said on Thursday that talks between Russia and Western powers aimed at ending tensions in Ukraine have potential but warned that U.S. and allies are prepared to impose more sanctions on Russia.

U.S. President Barack Obama said on Thursday that talks between Russia and Western powers aimed at ending tensions in Ukraine have potential but warned that the United States and its allies are prepared to impose more sanctions on Russia if the situation fails to improve.

"I don't think we can be sure of anything at this point," he told reporters at a news conference. "There is the possibility, the prospect, that diplomacy may de-escalate the situation."

However, Obama said he has been in close consultation with European allies and that a new round of sanctions is ready to go if Russia fails to help restore order in the east and south of Ukraine.

"We have put in place additional consequences that we can impose on the Russians if we do not see actual improvement of the situation on the ground," Obama said.

Obama told reporters that Western powers would weigh Russia's actions in the coming days before making any decisions about further sanctions.

Obama's comments to the media came after talks among the United States, Russia, Ukraine and the European Union led to a call for an immediate end to violence in Ukraine, where Western powers believe Russia is fomenting a pro-Russian separatist movement.