Ukraine’s President Volodymyr Zelenskiy has signed a law allowing reservists to be called up for military service without announcing mobilization, his office said on Wednesday, according to Reuters.

Approved by parliament late in March, the measure makes it possible to significantly boost the armed forces, amid escalation of tension with Russia in eastern Ukraine.

“This will make it possible to quickly equip the military units of all defense forces with reservists, thereby significantly increasing their combat effectiveness during military aggression,” the office said.

On Tuesday, Zelenskiy challenged his Russian counterpart, Vladimir Putin, to meet him in the Donbass region for talks to end the conflict there and ease tension between the neighbors.