Ukrainian President Volodymyr Zelensky has signed into law a bill lowering the military mobilisation age by two years from 27 to 25.
Kyiv has faced heavy losses on the battlefield after two years of war, whereas Russia has benefited from a sizeable advantage in manpower.
The move will allow Ukraine to call up more people to replenish its reserves, after volunteer numbers dropped.
Mr Zelensky said in December that 500,000 more soldiers were needed.
Although the bill was voted through by MPs in May 2023, it did not come into force because Mr Zelensky did not sign it.
It was not immediately clear what prompted the president to sign the bill on Tuesday, however he has previously warned of plans Russia may have to launch a spring or summer offensive this year.
Mr Zelensky’s signing of the bill could signify Ukraine’s effort to build up strong defensive fortifications in preparation for a Russian offensive