Ukrainian and U.S. officials accused Moscow of sending heavily armed columns across the border into Ukraine on Wednesday — a move that Washington says is likely part of a “Russian-directed counteroffensive” against Kiev.

During a press conference in Washington on Wednesday, U.S. State Department spokesperson Jen Psaki said reports indicated that “additional columns of Russian tanks, multiple rocket launchers, and armored vehicles” entered southeastern Ukraine this week, sharply escalating the five-month-old conflict.

“These incursions indicate a Russian-directed counteroffensive is likely under way in Donetsk and Luhansk. Clearly, that is of deep concern to us,” Psaki told reporters.

In Kiev, military spokesman Andriy Lysenko told the New York Times that an armored Russian column entered the town of Amvrosiyivka on Wednesday in what was likely an attempt to expand the current multipronged counteroffensive against Ukrainian troops.

Separatist forces have long claimed that they use weaponry captured from Ukrainian arsenals. However, American officials argue that the hardware in rebel hands includes highly sophisticated air-defense systems — equipment that the Ukrainian armed forces are not believed to posses, according to the Times.

Ukraine went on to accuse the Kremlin of directing troops toward the coastal city of Mariupol, in what appears to be a bid to draw Ukrainian forces away from the heavy fighting near the rebel strongholds in Luhansk and Donetsk.

The escalation of the conflict comes only hours after an inconclusive round of talks wrapped up between Ukrainian President Petro Poroshenko and Russian President Vladimir Putin in Belarus on Tuesday night.

Following the meeting, Putin described the increasingly violent war in Ukraine as a purely domestic affair.

“Frankly speaking, we cannot discuss any conditions for a ceasefire or possible agreements between Kiev, Donetsk and Luhansk,” Putin told reporters, according to a transcript published by his office. “This is not our business; it is a domestic matter of Ukraine.”

Putin’s remarks came less than 24 hours after Ukrainian authorities said they captured at least nine Russian paratroopers inside the country earlier this week.

Russian officials later went on to explain that the presence of members of an elite Russian airborne division in Ukraine was likely the result of an accidental incursion that occurred during a patrol.

Putin brushed off the incident — explaining that such incursions aren’t really that big a deal.

“After all, Ukrainian service members entered our territory with armored equipment,” said Putin. “And we didn’t have any problems.”

The U.N. estimates that more than 2,000 people have been killed since the pro-Russia uprising kicked off in April. The fighting has also displaced close to 400,000.

Contact us at letters@time.com.