Speaking on Tuesday on the sidelines of a NATO summit in Lithuania, French President Emmanuel Macron said the delivery of the missiles was aimed at enabling Ukrainian forces “to have the capacity to strike deeply”.

Macron did not specify what weapons would be provided, but French government officials told reporters that the president was referring to SCALP missiles, which can travel 250km (155 miles).

The announcement comes months after Britain began delivering its identical missiles, which it calls Storm Shadow, to Ukraine.

What is SCALP?

SCALP is a 1,300kg (2,870lb) missile armed with conventional explosives, usually launched from aircraft such as the British air force’s Eurofighter Typhoon or France’s Rafale.

Built by European manufacturer MBDA, it is the longest-range Western weapon supplied to Kyiv so far – three times of Ukraine’s capacities before Britain’s Storm Shadow delivery in May.

The missile is capable of striking targets far into the country’s Russian-occupied east, well behind front lines that have remained relatively fixed for months.

MBDA said on its website that the SCALP is “designed to meet the demanding requirements of preplanned attacks against high-value fixed or stationary targets such as hardened bunkers and key infrastructure”.

It has been used in a number of conflicts, including in Iraq, Libya and Syria.

How does SCALP operate?

The missile uses inertial navigation, GPS and terrain referencing to chart a low-altitude course to its target to avoid detection.

It also uses an infrared camera to match images of the target to a stored picture “to ensure a precision strike and minimal collateral damage”, MBDA said.

The warhead can be programmed to detonate either above the target in what is known as an airburst, on impact or after penetration.

Such capabilities are “critical for Ukraine’s forces to disrupt Russian logistics and command and control”, said Ivan Klyszcz, a researcher at the Estonia-based International Centre for Defence and Security.

SCALP attacks could help “with Ukraine’s current approach to operations, … namely to advance slowly so as to protect its forces and reduce its own casualties as much as possible”, he added.

What did France say?

While some Western allies are concerned that Ukrainian forces might conduct attacks into Russia itself, Macron’s comments implied that Paris had received assurances from Kyiv that the missiles would not be fired into Russia.

Speaking in Vilnius, he said the delivery of the missiles “would preserve the clarity and coherence of our doctrine, that is to say to permit Ukraine to defend its own territory”.

His message from Vilnius matched that of British Defence Secretary Ben Wallace, who said in May that Storm Shadow would “allow Ukraine to push back Russian forces based within Ukrainian sovereign territory”.

Macron did not say how many of the missiles would be sent, but a French diplomatic source told the Reuters news agency they were talking about 50 SCALP missiles.

France is understood to have an arsenal of fewer than 400, according to the defence magazine Defense et Securite Internationale.

The missiles would come from existing French military stocks, a French military source told the Agence France-Presse news agency, adding that it would be a “significant number”.

Separately, a French military source told Reuters the missiles were being integrated into Ukraine’s Russian-made fighter jets.

Rather than being an escalatory step, the source argued, the long-range weapons would help even up the balance of forces with Russia capable of firing much further. “It rebalances things and enables Ukraine to hit deep into Russian lines and can penetrate tougher targets,” the source said.

What has been Russia’s reaction?

Kremlin spokesman Dmitry Peskov warned that France’s decision to send the missiles “is a mistake” that would have harmful consequences for the Ukrainian side.

“Of course, that forces us to take countermeasures,” Peskov said.

Russia says Western arms deliveries to Ukraine cannot influence the course of the conflict, which Moscow refers to as a “special military operation”. They would only aggravate the fate of the “Kyiv regime”, Peskov said.

Russia had reacted with fury after the United Kingdom announced it would supply a batch of Storm Shadow missiles, warning that Britain risked being “fully dragged” into the conflict.