The situation in eastern Ukraine is actually quite serious, he said, adding a new escalation might occur any time despite a relative lull observed at the moment.
He noted such concerns are caused by "the approximation of fighting forces, armed separatists in the east and government troops."
"And they are now face to face. You also have an increased presence of heavy weapons directly in violation of the Minsk accord," the official added.
Walker recalled that the previous outbreak of violence near the towns of Avdiivka, Yasynuvata, Makiivka and Donetsk resulted in more than 30,000 cease-fire violations in a week or so, compared to less than 30,000 over the course of a month.
Many houses were obliterated in the fighting, the diplomat said, adding that the destruction of critical infrastructure facilities left locals without heating and water.