The package is the second this week, following another valued at $1 billion that was announced just after US President Joe Biden signed a much-delayed bill to provide new funding for Ukraine as it struggles to hold back Russian advances.

"I'm... pleased to announce today an additional commitment of $6 billion through our Ukraine Security Assistance Initiative," Austin told journalists, saying it will allow the procurement of new capabilities for Kyiv from US industry.

"This is the largest security assistance package we've committed to date," Austin said, adding that it will include air defense munitions, counter-drone systems, artillery ammunition and maintenance and sustainment support.

The United States has been a key military backer of Ukraine, committing more than $44 billion in security assistance since Russia launched its full-scale invasion in February 2022.

But prior to this week, Washington had announced new aid for Ukraine on just one other occasion this year, a $300 million package in March that was only made possible by using money that the Pentagon had saved on other purchases.

A squabbling Congress had not approved large-scale funding for Kyiv for nearly a year and a half, but eventually took action starting last week after months of acrimonious debate among lawmakers over how or even whether to help Ukraine defend itself.

The US House of Representatives on April 20 approved legislation authorizing $95 billion in aid funding, including $61 billion for Ukraine, while the Senate passed the measure on Tuesday and Biden signed it into law the following day.