Greece has rejected pressure from European allies to help Ukraine boost its air defences, arguing that Athens needs the systems for itself.
Ukraine’s Volodymyr Zelensky has appealed for another seven Patriots or similar defence batteries to protect its cities and power plants from Russian attack.
But Greece has said it cannot spare any of its Patriot or S-300 systems.
Reports say Spain will supply some Patriot missiles but not a full system.
Spain and Greece have come under pressure to help Ukraine from both Nato and European Union allies, in response to attacks on vulnerable cities including Chernihiv and power facilities in Kharkiv and close to Kyiv.
Ukraine only has a handful of Patriots to complement other Western missile defence systems and existing stocks of Soviet-era surface-to-air missiles (SAMs), such as the S-300.
Patriots are the most capable and expensive air defence systems that Ukraine has. Germany has already promised an extra Patriot system – and its defence and foreign ministers appealed to their counterparts earlier this month to respond urgently.
Nato chief Jens Stoltenberg has said allies have not provided the support that Ukraine was promised. And EU foreign policy chief Josep Borell said this week: “The Patriots are in the capitals. And it’s up to them to take the decisions.”
Greece in particular has stocks of Patriots and S-300s. But Prime Minister Kyrios Mitsotakis has ruled out handing any to Kyiv. “We were asked and we explained why we cannot do it,” he told Skai TV.
He explained his country’s air defences “are critical systems for the protection of Greek air space and will not be handed over to Ukraine”.
Athens has provided Kyiv with weapons and ammunition but is wary of losing any of its deterrent capability because of potential flare-ups with neighbour Turkey, even though relations at the moment are relatively stable.
Spain’s military has three Patriot batteries, but argues that it needs all of them and can only provide a “very limited number” of Patriot missiles because its reserve is relatively low, sources have told El País newspaper.
Each Patriot battery costs around $1bn (£800m), and each missile costs nearly $4m.
The continuing dilemma for Ukraine’s military commanders is where to place the missile systems, close to the country’s vulnerable cities or near the front line where Russia’s advances are most intense.
Recent Russian successes have been characterised by greater use of airpower. Su-34 fighter bombers have been dropping precision-guided munitions on Ukrainian forces.
We do not know where Ukraine place their SAM systems, but mitigating this growing Russian aerial threat might mean missile defence concentrates on the eastern front line.
That risks taking away a degree of missile defence for key cities and important areas of infrastructure – the sort of areas that have been regularly pounded by Russian cruise missiles and attack drones.
That is why Ukraine has been pleading for greater missile defences to plug the gaps in vulnerable areas.
Russia’s latest strikes have targeted Ukraine’s railway system in three different regions.
Rail operator Ukrzaliznytsia said three of its mechanics in their 20s and 30s were killed in a Russian missile attack while they were working in the eastern Donetsk region on Thursday. Russia says it hit a train carrying Western weapons.
Thirteen people were also wounded in a strike on a train station in Balakliya, in the Kharkiv region, and officials said a passenger train was 15m (50ft) from the station when it came under attack. In a separate Russian attack, rail infrastructure was damaged in the central Cherkasy region.
Meanwhile, Ukraine has had to pull back US M1 Abrams battle tanks from the front line, according to a report by the Associated Press.
Thirty-one Abrams tanks were originally provided to help Ukrainian forces operate on the battlefield, but Russia’s increased use of drones has made the tanks harder to protect and five have been lost, AP reported.