WASHINGTON — President Joe Biden's administration is urging Ukraine to quickly increase the size of its military by drafting more troops and revamping its mobilization laws to allow for the conscription of troops as young as 18.

A senior Biden administration official, who spoke on the condition of anonymity to discuss the private consultations, said Wednesday that the outgoing Democratic administration wants Ukraine to lower the mobilization age to 18 from the current age of 25 to help expand the pool of fighting-age men available to help a badly outnumbered Ukraine in its nearly three-year-old war with Russia.

The official said "the pure math" of Ukraine's situation now is that it needs more troops in the fight.

The White House has pushed more than $56 billion in security assistance to Ukraine since the start of Russia's February 2022 invasion and expects to send billions more to Kyiv before Biden leaves office in less than months.

But with time running out, the Biden White House is also sharpening its viewpoint that Ukraine has the weaponry it needs and now must dramatically increase its troop levels if it's going to stay in the fight with Russia.

The official said the Ukrainians believe they need about 160,000 additional troops, but the U.S. administration believes they probably will need more than that.

More than 1 million Ukrainians are now in uniform, including National Guard and other units.

Ukrainian President Volodymyr Zelenskyy has also been hearing concerns from allies in other Western capitals that Ukraine has a troop level problem and not an arms problem, according to European officials who requested anonymity to discuss the sensitive diplomatic conversations.

The European allies have also stressed that the lack of depth means that it may soon become untenable for Ukraine to continue to operate in Russia's Kursk border region that Ukraine seized this year. The situation in Kursk has become further complicated by the arrival of thousands of North Korean troops who have come to help Moscow try to claw back the land.

The stepped-up push on Ukraine to strengthen its fighting ranks also comes as Ukraine braces for President-elect Donald Trump to take office on Jan. 20. The Republican said he would bring about a swift end to the war and has raised uncertainty about whether his administration would continue the vital U.S. military support for Ukraine.