Vladimir Putin's forces are on the brink of overrunning Ukraine's army, a top US general has warned.

The stark warning comes as US Republicans in the House of Representative continue to stall attempts to pass a $60 billion military aid package for Kyiv.

The political stalemate has resulted in Ukraine's army facing a critical shortage of weapons, which has allowed Putin's army to regain the battlefield initiative.

Russian troops have intensified their attacks in recent weeks and are making gains along the entire frontline, despite the brave resistance of Ukrainian soldiers.

While those gains have been incremental, the pace of Russia's advance could soon gather pace and reach a critical point, the head of the US European Command told a Congressional Committee on Wednesday.

Commander General Christopher Cavoli said the tenacity and courage of Ukrainian soldiers was no match for Russia's superior manpower and weapons supply.

"If we do not continue to support Ukraine, it will run out of artillery shells and will run out of air defence interceptors in fairly short order," the General said.

"I can't predict the future, but I can do simple math,” he added.

"Based on my experience in 37-plus years in the U.S. military, if one side can shoot and the other side can't shoot back, the side that can't shoot back loses."

Ukraine has sought to use its drones to make up for the deficit in basic ammunition, achieving some success.

A NATO official told the publication Foreign Policy that drones had taken out around two-thirds of the Russian tanks destroyed over the last two months.

Despite this success, President Zelensky cautioned that drones could not replace air defence systems, long-range missile systems, or artillery.

The dire situation facing Kyiv's army was highlighted in graphic terms by General Cavoli.

"They [Ukraine] are now being outshot by the Russian side 5-to-1," he told US lawmakers.

“That will immediately go to 10-to-1 in a matter of weeks.

“We are not talking about months. We are not talking hypothetically,” he stressed.