President Volodymyr Zelenskyy of Ukraine, a video grab

Ukrainian president Volodymyr Zelenskyy on Wednesday called on allies not to let up pressure on Russia as he—for the first time—addressed the Ukraine Defence Contact Group meeting in Brussels.

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Mr Zelenskyy said that "a special situation" had emerged on the frontline in Ukraine, one "where it is important to put pressure [on Russia], non-stop".

"You all understand the principles of effective defence. It is the kind of defence that does not leave the enemy a chance to rest, regain strength, or choose some other tactics," he told defence chiefs of nearly fifty states at the NATO headquarters.

The Ukrainian president claimed that Russia had "lost the initiative" on the battlefield, and "it is Ukrainian courage and your support that determine what is happening on the battlefield and, most importantly, what will happen on the battlefield."

"And although the occupiers are still trying to storm our positions, and although the defence and our counter-offensive actions are very difficult, it is still Ukraine, it is our soldiers who determine the course of events," he said.

Earlier, the Ukrainian president said he believed the "last, most difficult" stage of Russia’s full-scale war against Ukraine had begun, and it was difficult to say when it would end.

The Ukraine Defence Contact Group started its 16th meeting on Wednesday in Brussels, where the United States and some other states are expected to announce additional military assistance to Kyiv.