Kyiv has been pleading for months for its supporters to send seven additional US-designed Patriot missile systems to help counter Moscow's attacks.

Since Ukraine stepped up its appeals, Germany has offered one more Patriot system, while Italy has promised a modern SAMP-T unit.

US media reported Wednesday that Washington would send another Patriot battery.

But US Defense Secretary Lloyd Austin refused to confirm that at a NATO meeting in Brussels Thursday.

"I don't have any announcements on Patriot batteries today, but what I can tell you is that I continue to work this," Austin said.

The Netherlands is spearheading an effort to construct a Patriot missile system out of different components from the stockpiles of various countries.

"We call it the Patriot puzzle -- that means that other countries are now looking into what they can do," said Dutch Defence Minister Kajsa Ollongren.

The Netherlands has promised to provide one radar and two launchers to help forge a complete system, she said.

German Defence Minister Boris Pistorius said: "We already provided three systems, that means a quarter of our capacity.

"So there is no space for providing even more than those three systems. Now it's on other partners to provide systems."

Several nations in NATO have the Patriot systems, with the US possessing by far the most.

Ukraine sees the Patriot as particularly valuable because it is one of the only systems capable of downing Russia's most advanced missiles.

Russia has exploited Ukraine's lack of air defences to pummel its troops at the frontline and devastate the country's power grid.

Ukraine's President Volodymyr Zelensky has said that Moscow has destroyed half of the country's electricity generation capacity since winter.

The Patriot is by far the most expensive single weapon system that the United States has supplied to Ukraine, according to the Center for Strategic and International Studies.

It estimates the total cost at around $1.1 billion: $400 million for the system and $690 million for the missiles.