Ukraine's new commander-in-chief of the armed forces has made his first public remarks since his promotion. General Oleksandr Syrskyi posted on social media on Friday that "only changes and constant improvement" will allow Ukraine to "achieve success" on the battlefield.

Syrskyi had previously served as the head of the ground forces. He said new technologies and modern strategies are crucial, and he stressed the need for quick delivery and distribution of weapons from allies overseas.

Syrskyi is taking the helm as the military struggles with a shortage of weapons and personnel. His troops have been trying to keep the Russians from capturing the entire Donetsk region in the east.

President Volodymyr Zelenskyy has been hesitant to call up thousands of new recruits as aid shipments from his Western allies stall.

Some Ukrainians say they are worried about the decision to shake up the military at such a crucial time in the war, even though Zelenskyy calls Syrskyi the country's "most experienced commander."

Leaders in Russia say the change will not affect what they call their "special military operation."

Former president Dmitry Medvedev called Syrskyi a "traitor" because he was born in the Soviet Union and trained in Moscow. Medvedev expressed his "hatred, contempt and disgust" and accused the commander of "destroying his loved ones."