WASHINGTON (AP) - The Obama administration says any Russian threat to Ukraine's navy would be a "dangerous escalation" of an extremely tense situation .
The State Department says Monday Washington would hold Moscow directly accountable for such an escalation but did not elaborate on potential consequences. But department spokeswoman Jen Psaki adds that she could not confirm if Russia had in fact made such threats.
Earlier Monday, a Ukrainian military spokesman said Russia had issued an ultimatum to the crews of two Ukrainian warships in Crimea, demanding that they immediately surrender or be stormed and seized.
Secretary of State John Kerry is leaving for Ukraine late Monday and then will travel to France and Italy. He had planned to see his Russian counterpart in Paris, but Psaki said that meeting was no longer certain.