* Tactics on ground suggest arm's-length approach from Moscow
* Some militants say they are Russian, but unclear from where
* Crimea-style annexation harder, may not be Russia's goal
* Moscow denies any involvement in Ukraine unrest
By Thomas Grove
SLAVIANSK, Ukraine, April 16 (Reuters) - There are important differences between Russia's intervention in Crimea and the events unfolding this week in eastern Ukraine which suggest Moscow has adapted its Crimea playbook and may be pursuing a different outcome.
Unlike the Black Sea peninsula, where thousands of Russian troops were already based at ex-Soviet naval facilities leased from Ukraine, there is little clear evidence of Moscow deploying significant forces on the ground in the east of the country.
In eastern towns where armed, pro-Russian rebels have seized public buildings and raised the Russian flag, some gunmen identify themselves to journalists as "Russians" - but that says little about citizenship in Russian-speaking parts of Ukraine.
They appear to be irregulars. If adept at barricading town halls, they lack the elite kit and well-drilled bearing of forces in Crimea - some of whom identified themselves to Ukrainian soldiers as Russian troops, despite Moscow's denials.
If Russia is playing a role on the ground in eastern Ukraine - something the Kremlin has again strenuously denied in the face of accusations from Kiev and the West - it is more arm's length than it was in Crimea, and annexation may not be its objective.
Crimea, attached to the mainland only by narrow strips of land and home to an ethnic Russian majority, differed in being easy to seal off against Ukrainian reinforcements and in having a greater likelihood of support among local residents for Russia to take over. Unlike the regions of Donetsk and Luhansk, Crimea was Russian in Soviet times until given to Ukraine in 1954.
What hand Moscow has in the unrest in Ukraine is a crucial issue in a crisis that has sunk relations between Russia and the West to their lowest level since the Cold War ended in 1991.
A U.S. defence official, speaking on condition of anonymity, said that separatists were wearing Russian uniforms without insignia and that Washington was not yet sure who they were:
"It looks and feels a lot like Crimea in terms of their behaviour and movements, but it's far from clear exactly who they are," the official said. "We're far more concerned about their activities than their identities."
As in Crimea, Russia says those taking up arms in Ukraine's industrial heartland are locals fearful of those who seized power in Kiev - a government Moscow says includes "fascists" bent on oppressing Russian-speakers. It denies accusations of funding and coordinating protests using agents or, as one Ukrainian minister said, an elite unit of its special forces.
While such denials - and the removal of uniform insignia -cut little ice with critics of last month's operation in Crimea, where Russian troops could be seen driving out of their local bases and landing from assault ships, there does seem to be a Russian effort to avoid an obvious troop presence in the east.
Russia may want to avoid an overt presence, which unlike in Crimea could only be achieved by rolling over the frontier in a way that could provoke a clearer Western backlash.
The Kremlin may not want to annex that part of Ukraine - an objective that the geography and demographics of the east would make harder than in Crimea.
Kremlin-watchers say President Vladimir Putin may have a more modest objective - to force Kiev and its Western backers to accept a new constitution that would give more autonomy to the eastern regions within Ukraine, and so prevent the country pulling out of Moscow's sphere of influence.
"Eastern Ukraine is completely different, both historically, and in terms of the do-ability of" annexing the region, said Tony Brenton, a former British ambassador to Moscow. "It's much bigger, it's much less pro-Russian, it has no clear borders.
"It would be harder to take and harder to hold," he told the BBC. "I am sure the Russians are not intending to do the same thing there."
One Russian objective in intervening could be to influence a presidential election Ukraine is holding on May 25.
Western military experts say that, in eastern Ukraine, Russia may have opted for a more covert approach, using agents to organise local militias and direct them towards targets, then move on before their presence became public knowledge.
They would not need to bring in weapons across the border because rifles and ammunition could be taken from police stations and security headquarters which they occupy.
Russian state television last year publicised the creation of a special army undercover unit trained to adopt enemy uniform and operate in hostile territory with the aim of "destabilising the situation, including via third parties".
Two locations, Slaviansk in eastern Ukraine, and Simferopol in Crimea, illustrate differences in tactics being employed.
The headquarters of the autonomous Crimean regional government in Simferopol was taken over in February by men who stood out from local pro-Russian militias who made up the bulk of those involved in events. They did so for one reason above all: each man in the unit had identical equipment down to the smallest detail, including boots, body armour and knee-pads.
These men, it became apparent to those observing them, were soldiers from the Russian army.
In Slaviansk, where militants last week took control of buildings and skirmished with forces loyal to Kiev, many of the gunmen also had matching uniforms and seemed well drilled.
Yet there were small differences: within one unit on the outskirts, one man had a knitted white sweater poking from under his camouflage tunic; some had elbow pads while others had pads on their knees; some flak jackets were black, others green.
Members of another unit, occupying the city council offices, were evasive about their identity. One said he was Russian and added: "We established order in Crimea and then we came here."
But quite what he meant by "Russian" is unclear. A third or more of the 4.5 million people in the Donetsk region identify themselves as ethnically Russian as opposed to Ukrainian. And most people in the east speak Russian as a first language.
As for his suggestion of having been in Crimea, that may be just another feint in the much wider information war being waged between Moscow, Kiev and anxious neighbours looking on.
The Ukrainian state security service (SBU) issued what it said was an audio recording of a phone call among three men discussing the killing of an SBU officer near Slaviansk on Sunday. The three spoke in accents distinctive to Russia and their exchange suggested they had been involved in the incident.
Some armed men in Slaviansk identified themselves to reporters as Cossacks from the "Terek Wolf Hundred" - a name derived from a river in the Caucasus where their frontiersman ancestors guarded and expanded the empire for Russia's tsars.
Their descendants have provided freelance militia services to the modern Russian state - though others also took part in the overthrow of the Moscow-backed president in Kiev.
Crimean Cossacks have played a prominent role in their own region backing the new, pro-Russian administration there. And in Donetsk, a spokesman for the separatist Donetsk People's Republic said Cossacks from Crimea were active in Slaviansk.
NATO Secretary-General Anders Fogh Rasmussen said on Tuesday "Russia's hand is deeply engaged". But Russian Foreign Minister Sergei Lavrov insisted: "Ukraine is spreading lies that Russia is behind the actions in the southeast." (Additional reporting by Richard Balmforth in Kiev, Gabriela Baczynska in Donetsk and Missy Ryan in Washington; Writing by Conor Humphries and Christian Lowe; Editing by Alastair Macdonald)