Pavlo Klimkin said in an interview with The Associated Press that Russian military and special forces are "in full command" in the rebel-controlled eastern regions of Donetsk and Luhansk. Following Ukraine's capture on July 25 of a Russian truck filled with weapons that was driven by a Russian military officer, Russia has scoffed at the allegations while pro-Russia rebels dismissed the Ukrainian claim as a fabrication.

Klimkin said the rebels are persisting only because of Russian weaponry and military personnel crossing the border into eastern areas which the government doesn't control.

According to Klimkin, Ukraine reached "a point of no return" from the post-Soviet era after the revolution that began on Independence Square in the capital Kiev in November 2013, which led to the collapse of the pro-Moscow government then in power.

Ukraine’s top diplomat also noted that Ukraine is committed to undertake major reforms "to fully depart from this post-Soviet reality," including tackling corruption and decentralizing the country, with the goal of joining the European Union and becoming part of "the European family," Klimkin said.

"A democratic and European Ukraine is a nightmare for Russia," he said, but Ukraine won't be deterred.

Klimkin said Ukraine "can't win militarily," but it can be successful in the war because it has the support of an international community that views Russia as the aggressor.

Ukraine's Ministry of Foreign Affairs said earlier that Russian aggression against Ukraine has violated most of the fundamental principles and obligations of the Organization for Security and Co-operation in Europe (OSCE).

The Kyiv government has had no control over parts of eastern Ukraine since Russian proxies began fighting government forces in April 2014. A conflict has already claimed more than 7,000 lives, according to the UN experts, and displaced more than 1.5 million people.