Briefing the Security Council, which met in the wake of Sunday's confrontation between vessels from the two neighboring countries off the coast of Crimea, DiCarlo urged them "to refrain from any ratcheting up of actions or rhetoric".
An "immediate de-escalation" of tensions is needed in the Sea of Azov and the Black Sea, she said, underlining the importance of "earnest attempts" to find a peaceful resolution to years of simmering conflict between Russia and Ukraine, Xinhua reported.
"(We) remind both (Russia and Ukraine) of the need to contain this incident so as to prevent a serious escalation that may have unforeseen consequences," she said.
Speaking to reporters before leaving the White House for campaign rallies, Trump said that "we do not like what's happening either way. And hopefully it will get straightened out".
He added that European leaders and the United States were working on the situation, noting "they're not thrilled. They are working on it. We're all working on it together".
--IANS kk/sc