Ukraine has to make hard decisions about further mobilization of its citizens to repel Russian aggression, but these measures are critical, U.S. Secretary of State Antony Blinken has said.

"Mobilization. This is critical, because even with the money, even with the munitions, there have to be people on the front lines to deal with the Russian aggression. Ukraine has hard decisions to make about further mobilization, but these are necessary decisions," he told a press conference in Brussels on Wednesday.

The official added that the allies have a commitment.

"For every person, every soldier that Ukraine mobilizes, we are committed to making sure that they have the training and the equipment they need to effectively defend the country," he said.