Prime Minister Viktor Orbán said that in an "unprecedented" incident, a Hungarian opposition party has played an active role in an operation of the Ukrainian secret services.

PM Orbán said, in a video uploaded to Facebook after a meeting of the Defense Council, that he had convened the body after "Hungary experienced an unprecedented attack from secret services in the past days."

"The coordinated smear campaign against Hungary was launched by Ukraine with the aim of making our referendum initiative on [Ukraine's] EU membership impossible," he said.

"It has turned out that the Ukrainians have activated their Hungarian contacts to carry out the operation, and have launched an attack against the Hungarian Armed Forces with the help of a Hungarian party."

PM Orbán said the Hungarian services were prepared to see further operations by secret services until the referendum was closed, and pledged that "we will complete the referendum, because neither Brussels nor Kyiv can decide above the heads of Hungarians."