The first F-16 fighter jets to be delivered from the West will arrive in Ukraine within weeks, says a high-ranking military source.
He said the aircraft were due to be supplied for the war against Vladimir Putin’s forces by June/July.
Ukraine has sought US-made F-16 fighter jets to help it counter Russian air superiority during more than two years of conflict.
The source did not say who would supply the jets.
But a number of countries in the West have offered to send these planes, with America having backed the move.
The Netherlands last month handed over another three F-16 fighter jets to a training facility in Romania, where Ukrainian pilots and ground staff are being taught to fly and maintain the planes in battle.
The Netherlands has been one of the driving forces behind an international coalition to supply Ukraine with F-16s to strengthen its air defence against the Russian invasion.
America has backed sending the planes to Ukraine, with Denmark, Norway and Belgium also reportedly involved in the initiative.
Ukraine’s President Volodymyr Zelensky called the move a “breakthrough agreement” last year and said the planes would strengthen Ukraine’s air defences and help its counter-offensive against Russian forces.
But US officials have privately said the jets will not be a game changer when they eventually arrive after months of training, given the strength of the Russian air force and its defence systems.
The Dutch have promised to deliver a total of 24 F-16s for use in Ukraine.
Ukraine has also stepped up its drone warfare, using the unmanned aircraft to strike more than 900 miles deep inside Russia.
Military experts expect more Russian aircraft to be downed by Ukraine forces in coming weeks as more weapons arrive from the West.
Mr Zelensky has told how more military aid is being rushed to the frontline after America agreed a £48 billion package, Britain a further £500 million of support, and other allies are also providing more supplies to Kyiv.
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Putin’s army chiefs are seeking to gain more territory before the military aid can reach Ukraine forces and as drier conditions have made advances easier.
Russian troops launched an armoured ground attack on Ukraine’s northeastern Kharkiv region early on Friday, advancing one kilometre near the border town of Vovchansk in an effort to create a buffer zone, a senior military source said.
The assault opens a new front in the war more than two years since Russia’s full-scale invasion.
Fighting in the border areas of the Kharkiv region continued and Kyiv has sent more forces to the area as reinforcements, the defence ministry said.
“At approximately 5 am, there was an attempt by the enemy to break through our defensive line under the cover of armoured vehicles,” the ministry said.
“As of now, these attacks have been repulsed; battles of varying intensity continue.”
A senior Ukrainian military source said that Russian forces were aiming to push the Ukrainian armed forces as far back as 10 kilometres (six miles) from the Russian border and that Kyiv’s forces were trying to hold them back.
Russian units have also been seizing more land in the Donetsk province of the eastern Donbas region.
But they have been suffering heavy losses, according to the Ministry of Defence in London.