Ukraine’s President told his military yesterday to be prepared for the possibility of a “full-scale invasion” by Russia across the entire length of the joint border, a day after the worst fighting with Russian-backed separatists in months.

His address in Parliament was one of the first times Petro Poroshenko has used the word “invasion” to refer to Russia’s behaviour since the start of a separatist rebellion in the east in which the UN says more than 6,400 people have been killed.

Referring to a 12-hour firefight involving artillery on both sides on Wednesday when Ukraine says the rebels tried to take the town of Maryinka, Poroshenko said: “There is a colossal threat of a renewal of large-scale military operations from the side of the Russian-terrorist groups.”

“The military must be ready as much for a renewal of an offensive by the enemy in the Donbass as they are for a full-scale invasion along the whole length of the border with Russia.”

Ukraine and its Nato allies have long accused Russia of sending weapons and troops to fight on behalf of separatists who control part of two provinces in its east. Moscow, which seized and annexed Ukraine’s Crimea peninsula last year, denies its troops are participating in the eastern fighting.

Concentration of Russian troops near border is one and a half times greater than a year ago

A ceasefire has mostly held for the past four months, after the separatists spurned an earlier truce to launch an advance and seize more territory for their self-proclaimed state in what Russian President Vladimir Putin calls “New Russia”.

The joint border stretches for more than 2,200 km, most of it far from the area where there has been fighting.

Earlier, Ukrainian military officials said that five Ukrainian servicemen had been killed and 39 wounded in the fighting around Maryinka, which lies 23 km to the west of the rebel stronghold of Donetsk.

The rebels updated their own casualty toll to 21 dead – five civilians and 16 fighters - and blamed Ukrainian forces for indiscriminate shelling of populated areas.

The fighting went far beyond regular low-level skirmishing that has occasionally flared since the shaky ceasefire was brokered in February by the leaders of Ukraine, Russia, Germany and France.

The West and Kiev say Russia has failed to fulfil the terms of the peace deal worked out in Minsk, Belarus and say it must pull out its forces and stop arms deliveries to the separatists.

Moscow takes the side of the separatists, accusing Kiev’s forces of ceasefire violations.

Poroshenko, who was delivering his state of the nation speech, said 9,000 Russian servicemen were deployed on Ukrainian territory.

“The concentration of Russian troops near the state border is one and a half times greater than a year ago,” he declared.

Reuters journalists have reported a Russian military build-up on the frontier in recent weeks, with thousands of troops and heavy weapons.

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