US President Donald Trump has said he will send more Patriot air defence missiles to Ukraine in a necessary step to defend the country.
Mr Trump did not reveal the number of Patriots he planned to send to Ukraine, but said the US would be reimbursed for their cost by European and NATO allies.
But what are the weapons, and why is Ukrainian President Volodymyr Zelenskyy likely to welcome the announcement?
One of the US's most advanced defence systems
The Patriot, short for Phased Array Tracking Radar for Intercept on Target, is a mobile surface-to-air missile defence system developed by Raytheon Technologies.
It is considered one of the most advanced air defence systems in the US arsenal and has been in service since the 1980s.
A typical battery includes radar and control systems, a power unit, launchers, and support vehicles.
The system can intercept aircraft, tactical ballistic missiles and cruise missiles, depending on the interceptor used.
How do Patriot missiles work?
The system has different capabilities depending on the type of interceptor missile used.
The earlier PAC-2 interceptor uses a blast-fragmentation warhead that detonates in the vicinity of a target, while the PAC-3 family of missiles uses more accurate technology that hits the target directly.
It is not clear what kind of Patriot systems have been donated to Ukraine, but it is likely that Kyiv has at least some of the newer PAC-3 CRI interceptors.
The system's radar has a range of more than 150 kilometres, NATO said in 2015.
Although the Patriot was not originally designed to intercept hypersonic weapons and Raytheon has not yet confirmed if it is able to do so, in May 2023 the US confirmed Ukraine had used it to shoot down a Russian Kinzhal missile, which Moscow claims is hypersonic.
Since January 2015, the Patriot has intercepted more than 150 ballistic missiles in combat operations, Raytheon says on its website.
Missiles used by 19 countries
Raytheon has built and delivered over 240 Patriot fire units, according to its website.
These have been shipped to 19 countries, according to Raytheon, including the US, Germany, Poland, Ukraine, Japan, Qatar, Saudi Arabia and Egypt.
In January, Axios reported the US had transferred about 90 Patriot interceptors from Israel to Ukraine.
A cost of more than $1.5 billion
A newly-produced single Patriot battery costs over $US1 billion ($1.5 billion), including $US400 million ($610 million) for the system and $690 million (around $1 billion) for the missiles in a battery, according to the Center for Strategic and International Studies (CSIS).
Patriot interceptors are estimated at around $US4 million ($6.1 million) per missile, CSIS says.
Why does Ukraine want Patriot missiles?
Kyiv has consistently asked Western allies for more air defences to protect critical infrastructure and civilian areas from frequent Russian missile and drone attacks.
While effective at intercepting missiles and aircraft, Patriots are a costly way to shoot down low-budget drones.
Still, Ukrainian officials say they are essential to defending key targets from Russia's escalating long-range attacks.
Russia says it sees the Patriots as a direct escalation.
Foreign Ministry spokeswoman Maria Zakharova said in May that supplying more systems to Ukraine would delay the chances of peace.
Trump's support for Ukraine still 'unpredictable'
Professor of International Security at the University of Birmingham, Stefan Wolff, told ABC's The World that the US is not providing enough missiles for it to be a "major game-changer".
"What it will do for Ukraine though is potentially increase a little bit of its air defence capabilities, where the country has been exposed to very large-scale Russian attacks," Mr Wolff said.
He said this decision was overall a positive sign that the US administration "has not completely turned his back on Europe and Ukraine".
"On the other hand, it shows [Trump's] approach to foreign policy is very, very unpredictable," he said.
"So even if today he decides he will send more Patriot missiles, tomorrow he might decide that he will relax permissions for Ukraine to use offensive weapons deeper inside Russia.
"All of this could again all change … we do not have the degree of predictability that I think above all Ukraine and Europe would really appreciate from the US administration."
Reuters/ABC
