Ukrainian President Volodymyr Zelenskyy is set to visit the White House for talks with Donald Trump, with the supply of US Tomahawks expected to be on the agenda.
Mr Trump had dangled the threat of sending Kyiv the long-range missiles if Russia did not return to peace talks.
"I might say, 'Look: if this war is not going to get settled, I'm going to send them Tomahawks,'" Mr Trump told reporters aboard Air Force One this week.
"The Tomahawk is an incredible weapon, very offensive weapon. And honestly, Russia does not need that."
With a range of up to 2,500 kilometres, the missiles could reach anywhere within Russia, including Moscow, putting thousands of military sites at risk.
The Kremlin warned that supplying Tomahawks would be "a new step of aggression" that could lead to a "very dramatic moment" in the war.
Then on the eve of his meeting with Mr Zelenskyy, Mr Trump announced he had spoken to Russian President Vladimir Putin, who agreed to meet to discuss ending the conflict.
In the surprise call, the Kremlin said Mr Putin stressed that selling Tomahawks to Ukraine would "inflict significant damage" to US-Russia relations and endanger peace efforts.
So what are the missiles being used to push Russia to the negotiating table?
How Tomahawks differ
The Tomahawk Land Attack Missile is the latest high-profile weapon sought by Ukraine, because it would significantly extend Kyiv's ability to launch precision strikes.
It was seen as a major step when the US gave Ukraine permission to use its long-range Army Tactical Missile Systems — known colloquially as ATACMS — on targets inside Russia in November last year.
ATACMS have a range of about 300km.
Analysts at the Institute for the Study of War, a Washington-based think tank, determined that at least 1,900 Russian military targets would be within range of a 2,500km variant Tomahawk.
About 1,655 key sites would be within range of the 1,600km variant, including the Yelabuga factory where Russia has been mass producing the Shahed attack drones being launched at Ukraine in record numbers.
Ukrainian forces have mainly been relying on long-range drones in recent months to conduct a series of strikes on oil refineries deep inside Russia.
Ukraine said its drones reached 1,400km beyond the front line to hit Russia's Bashneft oil refinery over the weekend, causing explosions and a fire.
The strikes have caused damage and interruptions to oil supplies, but analysts say drones alone are not capable of destroying key targets.
"Ukrainian forces are able to conduct long-range drone strikes against a significant portion of Russia's rear, but the payloads on these drones are limited and not suitable to destroy specialised objects," according to analysis by the Institute for the Study of War (ISW).
Ukraine says its FP-1 long-range attack drone — frequently used in attacks on Russia's oil refineries — is capable of carrying a warhead weighing up to 120 kilograms.
Tomahawks are precision-guided missiles about 6 metres long, weighing 1,500kg, and can carry a payload of about 450kg.
"Ukraine's ability to launch missile strikes deep into Russia's rear with larger payloads would allow Ukraine to significantly damage — if not destroy — key military assets in Russia, such as the Shahed drone factory in Yelabuga," the ISW said.
Ukraine has been developing its own long-range cruise missiles, such as the Neptune with a range of about 965km, and the Flamingo which can reportedly reach as far as 3,000km.
But Retired US Air Force Colonel Cedric Leighton said production capability and supplies were an issue.
"They don't have enough of those weapons and sometimes the accuracy of those weapons can be thrown off by things like jamming," he told ABC Radio National Breakfast.
Tomahawks not a 'magic bullet'
Marcus Hellyer, head of research at defence think tank Strategic Analysis Australia, said Tomahawks had better range and precision, but he was sceptical about the overall impact.
"There is this sort of weird obsession with the Tomahawk," he told the ABC.
"I'm not sure it is necessarily that deserved nowadays."
Tomahawks have been produced for more than 40 years.
Although the missiles have undergone various upgrades, Dr Hellyer said they were still based on previous generation technology and were not particularly "survivable".
"It's not fast or stealthy," he told the ABC.
"The Tomahawk is a cruise missile, so it flies low, not very high above the ground.
"This was really cool a while ago, but modern air defence networks are getting really good at defending against those threats."
Justin Bronk, senior research fellow at the Royal United Services Institute (RUSI), said Tomahawks could help put pressure on Russia's air defences, but were no "magic bullet".
"They can be intercepted like any other cruise missile, and it's unlikely they would suddenly make a strategic difference to the dynamics of the war in its fourth year," he told the Kyiv Independent.
Russia has air defence systems such as the S-400 which would be capable of taking out Tomahawks.
Dr Hellyer said some missiles could get through and damage key sites, but for Tomahawks to make a significant difference the US would need to provide Ukraine with "thousands".
"You'd need a lot, because the Tomahawk doesn't have a particularly large warhead," he said.
What Russia is saying
As Tomahawk talk gained momentum in recent weeks, Russia responded with a series of threats.
Kremlin spokesperson Dmitry Peskov said the issue of Tomahawks was causing "extreme concern" in Moscow, adding that the war was now entering a "dramatic moment".
Mr Putin said earlier this month that it was impossible to use Tomahawks without the direct participation of US military personnel, so any supply to Ukraine would trigger a "qualitatively new stage of escalation".
The threatening rhetoric was similar when the US was considering sending Ukraine ATACMS missiles, F-16 jets, and Abrams tanks — all of which were delivered without major escalation.
Dr Hellyer does not think the story will change with Tomahawks.
"I think there's a lot of bluster," he said.
Mr Trump said Mr Putin agreed to meet in Budapest for another summit on the war in Ukraine, after what he called a "very productive" phone conversation on Thursday, local time.
A date for the meeting has not been set, but Mr Trump said it was likely "within two weeks or so".
Mr Zelenskyy, who is expected to meet Mr Trump in Washington on Friday seeking more military aid, attributed the progress to the Tomahawks threat.
"We can already see that Moscow is rushing to resume dialogue as soon as it hears about Tomahawks," he wrote on X.
Mr Trump said the Russian leader "didn't like it" when he raised the possibility during their call of giving Ukraine the missiles.
He has since appeared to cast doubt on giving Kyiv the highly sought-after weapons, saying the US could not "deplete" its own supply.
"We need them too, so I don't know what we can do about that," he said.
ABC/Wires
