Biden signs Ukraine aid bill, promises military shipments in 'hours'

US President Joe Biden said fresh military aid will begin flowing to Ukraine "in the next few hours" after he signed into law a hard-fought bill that provides for billions of dollars in new spending to support Ukraine's fight against Russia.

"I'm making sure the shipments start right away. In the next few hours - literally in a few hours - we are going to begin sending equipment to Ukraine for air defence munitions, for artillery for rocket systems, and armoured vehicles," he said at the White House.

Biden said replenishing Ukraine's inventories of US weapons was an investment "not only in Ukraine's security" but also Europe's and "our own."

Biden warned that if Ukraine fails, Russian President Vladimir Putin's next step could be a "direct attack" on a NATO ally: "We'd have no choice but to come to their aid. Just like our NATO allies came to our aid after the September 11 attacks."

Senators in the US Congress gave their approval for a $61-billion aid package for Ukraine after the House of Representatives gave its OK following months of political wrangling and strident opposition from far-right Republicans.

Little material support had been given to Kiev from Washington since late last year due to the deadlock, despite urgent pleas from Ukrainian President Volodymyr Zelensky.

"America stands with our friends, we stand up against dictators, we bow to no one, to no one — certainly not Vladimir Putin," Biden said, although he noted that aid package should have arrived at his desk "sooner."

The billions in security assistance approved by Congress and signed by Biden include funds to increase the number of weapons and ammunition in the US military's inventory.

This money therefore only goes indirectly to Ukraine, as the US usually equips Kiev with equipment from its own stocks - which is often quicker than ordering new equipment from the defence industry.

Biden said on Wednesday that Ukraine will once again receive military equipment from US stockpiles.

Other parts of the package are earmarked for financial assistance, partly in the form of loans.

The text of the legislation also urges the delivery of long-range ATACMS missile systems. To date, the US has delivered ATACMS with a range of around 165 kilometres, however Ukraine wants ones with a range of 300 kilometres.

Biden and Zelensky spoke on the phone on Monday. Afterwards, Zelensky said that details on the delivery of more ATACMS had been "finalized." He did not specify which model the US would supply.

Republican hardliners in Congress vehemently oppose further US aid for Ukraine, arguing that taxpayers' money should first and foremost be spent on protecting the country's own border with Mexico.