Ukrainian border guards stand grim-faced and nervous at the remote Marynivka checkpoint on the frontier with Russia, fearing an attack by pro-Moscow separatists at any time.

Last week they fought off an assault by up to 150 rebels seeking control over supply routes from Russia to bring in arms and other war materials, forcing them to abandon two armoured personnel carriers strafed with machinegun fire.

A weary border guard, wearing a camouflage T-shirt and a cap with a Ukrainian national emblem, said he feared the worst if the authorities in Kiev did not send help.

“They told us to expect reinforcements. We’re hoping for them soon,” said the guard, who gave his name as Vadim. “They (the separatist rebels) drove around us in circles shooting for about four or five hours.”

An unexploded rocket-propelled grenade lay in the long grass 200 metres from the border post.

Not all border guards have put up such a fight. Outgunned and outnumbered, they have fled one post after another in the week since the rebels took the border guards’ headquarters in Luhansk, the region’s main city.

In an angry letter to the country’s defence minister, frustrated Luhansk border guards wrote: “We, including eight among us wounded by bullets and grenades ... sincerely waited for help from you but it never came.”

Some of the rebel fighters, who hope to join territory in Russian-speaking east Ukraine with Russia, say they are already able to navigate the border with impunity.

“We need guns, we need supplies from Russia,” said a tired-looking rebel, smoking pungent cigarettes in a cafe in the city of Donetsk. He asked not to be identified, fearing punishment if his side loses the conflict.

We need guns, we need supplies from Russia

Ukraine’s inability to police parts of its own border underscores the military weaknesses President Petro Poroshenko has to deal with as he tries to end the insurrection that began after his Moscow-leaning predecessor was toppled in February.

His promise to regain Crimea, annexed by Russia in March, also puts him at loggerheads with President Vladimir Putin, complicating dealings with Moscow to plug the power vacuum at the border where Kiev says Russia gives rebels a green light.

“The border can’t be closed in a day, and without that the anti-terrorist operation (against the separatists) could continue endlessly,” Ukrainian military expert Dmitry Tymchuk wrote on Facebook.

The remaining frontier posts held by Ukraine – built for customs controls, not for war – lie on the outer edge of a swathe of territory crisscrossed by separatists’ roadblocks that juts into Russia.

At one backwater border crossing that has fallen to the separatists, at Chervonopartizansk, rebels wave through a steady trickle of cars. One, dressed in a traditional Cossack fur hat who gave his name as Alexander, said the border guards there had left in a long convoy, taking their weapons and families with them.

“We let them go with their weapons to avoid a fight. Since their position was weaker, we would have had to kill them,” he said with a gold-toothed grin.

That may not be an idle threat. Five of the rebels are middle-aged miners but all were ex-military, including veterans of the 1979-1989 Soviet war in Afghanistan.

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