US Secretary of State John Kerry said Saturday that new "serious sanctions" against Russia were being considered over the conflict in Ukraine.
"In the next few days I anticipate that President Obama will evaluate the choices that are in front of him and will make his decision," he told a press conference in London.
"I am confident that some additional steps will be taken in response to the breach of this ceasefire."
Kerry said that a truce brokered by Germany and France had been honoured by pro-Russian separatists in only "a few areas".
"If this failure continues, make no mistake, there will be further consequences including consequences that will place added strains on Russia's already troubled economy," he added.
On Saturday, members of Ukraine's military and pro-Moscow rebels swapped scores of prisoners in a rare act of compliance with the truce, brokered in Minsk earlier this month.