Ukraine has been urging its Western allies for permission to use their supplied long-range missiles to strike deep into Russia for months, claiming it needs these munitions to target military sites that store Russian warplanes and missiles used amid their ongoing conflict.

This contentious request was discussed in Friday's meeting between US President Joe Biden and UK Prime Minister Keir Starmer, with the latter pushing Washington to provide more leeway to Ukraine. Additionally, Starmer especially seeks Biden's support to allow Kiev to use British Storm Shadow missiles in Russian territory.

The meeting concluded with the White House suggesting a "holding pattern" until Ukrainian leader Volodymyr Zelensky visits New York later this month to present his "victory plan."

So what exactly are these weapons?

Storm Shadows and SCALPs

Known as Storm Shadows in Britain and SCALPs in France, the two nations have sent Kiev air-launched cruise missiles that have attacked Russian targets in the Black Sea and Crimea.

These missiles have a range of around 250 kilometers, and have been launched from Ukraine's Soviet-era fighter jets.

The UK is aiming to obtain approval from the US to authorize Ukraine's use of the missiles across the border with the intention of the allies presenting a united front.

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For its part, France has previously expressed support for Kiev's deep strikes into Russia, on the condition they target military sites directly linked to Moscow's war efforts against Ukraine. 

Some analysts speculate the United States is following its pattern of allowing its allies to take the initial actions in providing Ukraine with new capabilities or permissions, with Washington later potentially following suit.

ATACMS

The Army Tactical Missile Systems, or ATACMS (pronounced "attack 'ems"), are US-made long-range missiles composed of 170 kilograms of explosives. Depending on the model, the missiles can strike targets at a range of 305 kilometers.

Despite Washington providing Kiev with ATACMS last year, the Biden administration has withheld its authorization to use the munitions to strike deep into Russia.

US and European military officials stated that, in anticipation of potential approval, Russia moved 90% of its air bases that store bomber jets out of the missile's range.

Initially developed in the 1980s to hit Soviet targets deep into enemy territories, ATACMS could also be used to strike Russia's ground-based air defense systems that can target Ukraine's new batch of F-16 fighter jets, experts said.

JASSMs

Joint Air-to-Surface Standoff Missiles, known as JASSMs (pronounced “jazz ’ems”), are air-launched missiles that can strike as far as 370 kilometers.

These missiles also contain 450 kg warheads that can be fired from F-16 fighter jets, allowing Kiev to fire deep into Russia without leaving its own airspace. 

These long-range missiles have not yet been supplied to Ukraine. However, according to a US official, the Biden administration is considering providing them amid the conflict.

The official added that even if Biden approves the provision of these munitions, delivery could take months, and it remains unclear if the US president would allow Ukraine to use them to strike into Russia.