Ukraine crisis: the border hunt for Vladimir Putin's hidden army

But the Russian invasion force - if it is here - is very well camoflaged. As the fog lifted, murky shapes were revealed as trees, houses and old Lada cars. No tanks emerged from the gloom, no suspicious flights of helicopters passed overhead, and no green painted trucks rumbled down the roads.

In a 200 mile trip along the border region, the only Russian armour on display in this flat landscape was of a much older vintage, and stood on plinths in town squares.

The war memorial T-34s, which won one of the biggest tank battles in history here in Kursk in 1943, do not look as if they are about to roll off their pedestals and head west into Ukraine.

Only President Vladimir Putin knows if the hidden army will get the order to march. If so, the outcome will be much bloodier than the almost entirely peaceful seizure of Crimea.

If that operation is a reliable template, any invasion would be aimed at seizing 'friendly' portions of eastern Ukraine with high Russian or Russian-speaking populations. The goal would be to redraw the frontier, daring Ukraine's new government - and the world - to do something about it.

Ukraine's entire army totals only 65,000 troops, compared with almost 300,000 in Russia's western and southern military districts alone. Nonetheless, Ukraine has deployed its own forces in the east and promised to resist any Russian attack.

Although Ukraine's eastern regions of Kharkiv, Donetsk and Lugansk are strongly Russian-speaking, the 2001 census shows that Ukrainians still comprise the majority in all three areas. That would present Russia with the challenge of controlling a large territory with a potentially hostile population.

As in Crimea, an attack would probably begin with special forces and airborne troops seizing key points, including administrative buildings, airports and bridges. Unlike in Crimea, tanks and mechanised infantry would then sprint across the border to provide rapid reinforcement, under cover of air strikes and artillery bombardments.

Where these spearheads stop would depend on where Mr Putin chose to draw his new frontier. Likely targets include the cities of Kharkiv, Donetsk, and Lugansk - all places that have seen pro-Russian demonstrations, and all within striking distance of the border.

While a march on the capital, Kiev, seems unlikely, Russian forces based in the Rostov region may launch a blitzkrieg along Ukraine's south coast to open a land corridor to Crimea.

In Kiev's nightmare scenario, that offensive would roll onwards to seize Odessa and join Russian forces in the breakaway region of Transdniester, leaving Ukraine landlocked.

But the moment for action may not yet have arrived. The landscape here consists of vast fields, as flat as a billiard table, intersected by small rivers and served by poor roads.

It is almost perfect tank country, as local history testifies. But the rich earth may still be too boggy - and the rivers too high - to provide a decent surface for Russia's heavy T-90 tanks.

Winter has been remarkably short and the ground could dry within days or weeks rather than months. But each lost day represents more time for Ukraine to prepare.

While the army is keeping well out of sight for now, local security services are on edge. In one sleepy border town, the local police and the FSB security service were sufficiently alarmed by the sight of strangers photographing a statue of Lenin to take them in for a two-hour interview.

'Nonsense,' said the friendly man from what police call 'the other agency' when he learnt about the supposed military buildup. 'It's just after what happened in Ukraine people here are quite touchy about Lenin. They think someone might come across the border and pull him down.'