The next package is likely to include ATACMS missiles, which have already been sent in limited quantities to the front line, and Patriot missiles for Ukraine’s air defence systems.

The most recent round of aid, which was drawn from savings in the existing Pentagon budget, included munitions for the High Mobility Artillery Rocket Systems (HIMARS).

The US stores some 155 million howitzer rounds in Europe, and could send them to Ukraine within days.

The global supply of rounds began to fall in recent months after the US budget for Ukraine aid dwindled and European manufacturers were unable to keep up with demand.

William Burns, the director of the CIA, has said that without speedy assistance from the US, Ukraine could lose the war against Russia this year.

Despite initial plans for a spring offensive this year, Ukraine has resorted to defending its existing front lines against Russian troops, without the weapons or personnel to launch a new push into Crimea.

The military draft in Ukraine was this week lowered to include men aged over 25, from its previous level of 27.

As the war in Ukraine has progressed, the US has agreed to send increasingly expensive military systems to Kyiv, including the Abrams tank.