US President Barack Obama speaks to the media at the White House in Washington April 17, 2014. [Photo/Agencies]

Ukraine crisis

WASHINGTON - US President Barack Obama spoke cautiously on Thursday about an agreement on the Ukraine crisis and warned that Russia could face additional sanctions if situation fails to improve.

"I don't think we can be sure of anything at this point. I think there is the possibility, the prospect that diplomacy may de-escalate the situation," Obama told a press conference at the White House hours after a deal on Ukraine was reached following four-way talks in Geneva.

The United States, Russia, Ukraine, and the European Union concluded talks in Geneva on Thursday after signing a statement on the de-escalation of tension in Ukraine. It says all sides must refrain from any violence, intimidation or provocative actions as part of initial steps to restore order in the country.

"All illegal armed groups must be disarmed; all illegally seized buildings must be returned to legitimate owners," said the statement.

Obama said the question now is whether Russia will use the influence that it has exerted "in a disruptive way to restore some order" in Ukraine.

"My hope is that we actually do see follow-through over the next several days, but I don't think, given past performance, that we can count on that," Obama said.

"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," he said.

On Thursday, Obama discussed the development with German Chancellor Angela Merkel. The leaders urged Russia to "use its influence over the irregular forces in eastern Ukraine to get them to lay down their arms and leave the buildings they have seized," said a statement issued by the White House.

Obama also spoke by telephone with British Prime Minister David Cameron on the situation in Ukraine on Thursday. They said "they will look for the Russians to quickly follow through on their commitments in Geneva," said a separate statement from the White House.

The three leaders all agreed that the United States and Europe are prepared to take further measures if de-escalation in eastern Ukraine does not occur "in short order," according to the statements.

In addition, US Vice President Joe Biden, in a telephone talk with Slovakian Prime Minister Robert Fico on Thursday, said if Russia further escalated the situation in Ukraine, it would face mounting consequences. Biden also discussed the Ukrainian crisis with Bulgarian President Rosen Plevneliev later in the day.