The official did not say how many SCALP -- an air-launched British-French missile known to UK forces as the "Storm Shadow" and the longest-range Western weapon in Ukraine -- had been sent.

"The first missiles had been delivered when the president announced it," the source said, speaking at the NATO summit in Vilnius.

Macron said the new missile delivery was designed to allow Ukraine to strike at Russian occupation forces "in depth" during its counteroffensive to liberate its territory.

Kremlin spokesman Dmitry Peskov warned that France's decision to send the missile "is a mistake with consequences for the Ukrainian side, because this will of course force us to take countermeasures."

The SCALP/Storm Shadow has a range of 250 kilometres (155 miles) and Britain announced in May that it would supply a batch of the advanced weapons.

Russia reacted with fury, warning that London risked being dragged directly into the conflict, and even some Western allies were concerned that Kyiv might conduct strikes into Russia itself.

Macron implied, however, that Ukraine had given an undertaking not to use SCALP against such targets, saying that they had been given "in coherence with our doctrine, that is to say to permit Ukraine to defend its own territory".

Macron did not say how many of the missiles would be sent, but France is understood to have an arsenal of less than 400, according to specialist defence review DSI.

"The number delivered to Ukraine is fairly significant but it will preserve French stocks at a level comfortable above what we need," the military source said.

Rather than being an escalatory step, the source argued, the longer-range weapons would help even up the balance of forces, with Russia capable of firing much further.

The SCALP was designed to be fired from western fighters like France's Rafale or the British Typhoon, but Ukraine will modify it's Soviet-designed MiG jets to accept the weapon.