Russia is waging an undeclared war on Ukraine, punishing the country for its European choice, Ukrainian Foreign Minister Pavlo Klimkin has said.

"It is an undeclared war, with an unfair price, because we are fighting for justice and democracy on our own land. We are attacked for our European choice," he said at the Atlantic Council in Washington on Tuesday.

Klimkin said that Ukraine now comes under attack "more than ever."

"Thus, although the Ukrainian military significantly move further in liberating the territory, Russian-supported militants continue the occupation of Donetsk and Luhansk regions, and groups of Russian citizens with ties at the Russian security services form new criminal gangs, involve the local population in them with fraud and put pressure on those who refuse to obey them. They have the most modern weapons capable of shooting down even international airplanes. In addition, more often engaged in fighting are regular armed forces of the Russian Federation that shell the territory of Ukraine and invade its airspace," he said.

"In my opinion, the world faces the biggest threat since the Cuban crisis of 1962," he said.

Klimkin said that in order to resolve this conflict, it was necessary to have a deep understanding of the situation and respond to it not only in terms of de-escalation, but also in terms of the consequences for the future.