NATO’s Secretary General Jens Stoltenberg and Ukrainian President Volodymyr Zelenskyy on Wednesday discussed Kyiv’s recent gains against Russian forces as well as further steps on its admittance to the 30-member military alliance.

In a tweet after their phone conversation, Stoltenberg said he “praised the brave Ukrainian people and forces for the impressive progress in regaining their territory from Russian aggressor.”

He reassured Zelenskyy that “NATO will sustain and step up support for Ukraine for as long as it takes.”

Stoltenberg also reiterated NATO’s call for Russia to “stop the war it has started.”

Over the past few days, the Ukrainian army has achieved significant military successes on two fronts.

In the east, Ukrainian forces managed to take back control of Lyman, a railway hub in the Donetsk region, while also breaking through Russian defense lines in the south to advance along the Dnipro River.

At a news conference last week, Stoltenberg asserted that the war in Ukraine has reached a “pivotal moment.”

He said the partial mobilization in Russia, its illegal annexation of four Ukrainian regions, and nuclear threats indicate that the war “is not going according to plan” for Moscow.

Zelenskyy, for his part, said he is in constant contact with "our strategic partners."

"Had a phone call with NATO Secretary General Jens Stoltenberg. Coordinated further steps on the path of Euro-Atlantic integration of Ukraine,” he said on Twitter.

Last week, Zelenskyy announced a bid for fast-track membership of the NATO alliance, as President Vladimir Putin held a ceremony in Moscow to declare Ukraine's Donetsk, Luhansk, Kherson and Zaporizhzhia regions as part of Russia.

Referendums in the Russian-controlled regions, held last month, have been condemned and termed sham by the international community.

The Kremlin says Ukraine's intention to join NATO was one of the main reasons for Russia to start its war in February.