Obama presses Putin on Ukraine, warns of further "costs"

US President Barack Obama urged Russian President Vladimir Putin on Monday to support peace in Ukraine and said Moscow would face further "costs" if it did not take steps to reduce tensions in the country, the White House said on Monday.

"The president spoke to President Putin and once again urged him to support peace instead of allowing the provision of arms and materiel across the border and continuing support for militants and separatists who are further destabilizing the situation in Ukraine," White House spokesman Josh Earnest told reporters.

"Russia will face additional costs if we do not see concrete actions to de-escalate the situation," he said of Obama's message to Putin.

The two leaders spoke in a call earlier on Monday.

This comes after Britain's Foreign Secretary William Hague warned Russia that the European Union was ready to impose more sanctions over the crisis in Ukraine if necessary.     

Hague was speaking ahead of a meeting in Luxembourg of EU foreign ministers, who were expected to discuss the possibility of more sanctions ahead of a summit of EU leaders on Friday.         

"(Russian president Vladimir) Putin should be in no doubt that in the EU we are ready to take those measures," Hague told reporters. "A lot of work has gone on on preparing wider sanctions on Russia."

Also on Monday, Russian gas flows to Europe via Ukraine were stable amid pricing standoff between Moscow and Kiev, Russian gas pipeline exporting monopoly Gazprom said.         

Gazprom cut off gas supplies to Kiev last week after the Ukraine failed to pay off its gas debts. Gazprom meets around a third of Europe's gas demand, while half of Russian gas exports to Europe go via Ukraine.           

"Transit via Ukraine flows within contractual parameters, the volume for the past 24 hours has been at 205 million cubic metres," Sergei Kupriyanov, a Gazpom's spokesman said.

This comes after Russia's Finance Ministry said that it had not yet received a $73.3 million coupon payment on a $3 billion Eurobond from Ukraine that Kiev said it had paid on Friday.      

"Unfortunately, we cannot confirm as of now the receipt of the coupon payment," the ministry's press service told Reuters.       

"However, the terms of the bond provide for a 10-day grace period. We expect that the government of Ukraine will fulfil its obligations to pay the coupon during this period."         

Russia bought the eurobond in December under a financial aid package agreed with then-president Viktor Yanukovich, who was later ousted and replaced by a government much less sympathetic to Russia.