Last checked at 
(Adds reports of shooting, operation in Kramatorsk)
* Shooting reported in Ukraine's east
* Military operation begins against separatists
* Crackdown will be in stages, president says
* Ukrainian troops and APCs seen near flashpoint town
By Richard Balmforth and Gabriela Baczynska
KIEV/KRAMATORSK, Ukraine, April 15 (Reuters) - Ukrainianarmed forces on Tuesday launched a "special operation" againstmilitiamen in the country's Russian speaking east, authoritiessaid, recapturing a military airfield from pro-Moscowseparatists.
Gunfire could be heard from the airfield at the town ofKramatorsk after a fighter jet swooped low over the area.Ukrainian troops were seen disembarking from helicopters.
A Reuters correspondent in Kramatorsk saw four militaryhelicopters over the airport. Two of these landed and whentroops stepped out and walked across the field, locals manning abarricade shouted "Shame! Go back home!"
Ukraine's acting President Oleksander Turchinov had earlierannounced that a military operation was under way to flushpro-Russian separatists out of the government buildings andfacilities they have seized in about 10 towns and cities in theeast over the last few days.
Turchinov issued a statement saying Ukraine had retaken theairfield in Kramatorsk from pro-Russian militants, while thestate security service said an "anti-terrorist" operation was inprogress against separatists in the nearby town of Slaviansk.
The operations in Kramatorsk and elsewhere appeared to markan escalation of the deepest East-West crisis since the ColdWar. The standoff has raised fears in the West and in Kiev thatRussia might intervene militarily on behalf of Russian speakersin eastern Ukraine.
Earlier, pro-Russian militants holed up in the Kramatorskpolice headquarters since Saturday had left the building - but astate security official in Kiev said separatists had then takenover the agency's offices in the town.
SHARES FALL
The reports of military action in eastern Ukraine causedRussian shares to fall sharply, with the main Moscow indicesdown about three percent.
The crisis has also prompted fears that Moscow might turnoff gas supplies to Kiev, disrupting flows to the EuropeanUnion. Russian exporter Gazprom promised it wouldremain a reliable supplier to the EU, but German energy companyRWE began deliveries to Ukraine on Tuesday - reversingthe usual east-west flow in one central European pipeline.
Russian Prime Minister Dmitry Medvedev gave a gloomyassessment, apparently referring to the deaths of at least twopeople on Sunday when Kiev unsuccessfully tried to regaincontrol in Slaviansk, about 150 km (90 miles) from the Russianborder.
"Blood has once again been spilt in Ukraine. The country ison the brink of civil war," he said on his Facebook page.
Turchinov said an offensive he first announced on Sunday wasnow in progress after days in which it failed to materialise.
"The anti-terrorist operation began during the night in thenorth of Donetsk region. But it will take place in stages,responsibly, in a considered way. I once again stress: the aimof these operations is to defend the citizens of Ukraine," hetold parliament.
At least 15 armoured personnel carriers displaying Ukrainianflags were parked by the side of a road around 50 km (30 miles) north of Slaviansk, witnesses said.
Ukrainian troops wearing camouflage gear and armed withautomatic weapons and grenade launchers were stationed nearby,with a helicopter and several buses containing interior ministrypersonnel near the road.
In Slaviansk itself, separatists have seized the localheadquarters of the police and state security service.
BARRICADES
Outside the police station about a dozen civilians mannedbarricades of tyres and wooden crates. A dozen or so armedCossacks - paramilitary fighters who claim descent fromTsarist-era patrolmen - stood guard at the mayor's offices.Shops were functioning as usual and bread supplies were normal.
In Kiev, a radical pro-Russian candidate running forUkrainian presidential elections due next month was beaten up byan angry crowd.
Moscow accuses Kiev of provoking the crisis by ignoring therights of citizens who use Russian as their first language, andhas promised to protect them from attack. Russia also stressesthe presence of far-right nationalists among Kiev's new rulers.
However, a United Nations report on Tuesday cast doubt onwhether Russian-speakers were seriously threatened, includingthose in Crimea who voted to join Russia after Moscow forces hadalready seized control of the Black Sea peninsula.
"Although there were some attacks against the ethnic Russiancommunity, these were neither systematic nor widespread," saidthe report by the U.N. human rights office.
NATO Secretary-General Anders Fogh Rasmussen accused Moscowof involvement in the rebellions. "It is very clear thatRussia's hand is deeply engaged in this," he told reporters.
Russian Foreign Minister Sergei Lavrov denied that Moscowwas stirring up the separatists in the east and southeast as apossible prelude to repeating its annexation of Crimea. "Ukraineis spreading lies that Russia is behind the actions in thesoutheast," Lavrov said on a visit to China.
He called on Kiev to hold back before a meeting betweenRussia, the EU, United States, and Ukraine planned for Geneva onThursday. "The use of force would sabotage the opportunityoffered by the four-party negotiations in Geneva," he said.
Moscow has demanded constitutional change in Ukraine to givemore powers to Russian-speaking areas, where most of thecountry's heavy industry lies, while the rebels have demandedCrimean-style referendums on secession in their regions.
Kiev opposes anything that might lead to the dismembermentof the country. But in an attempt to undercut the rebels'demands, Turchinov has held out the prospect of a nationwidereferendum on the future shape of the Ukrainian state.
REVERSE FLOWS
RWE's deliveries of gas to Ukraine through a pipeline fromPoland marked an initial step in EU efforts to counter the riskthat Russia will turn off the taps.
Central Europe's pipeline network is designed to carryRussian gas westwards. But Polish operator Gaz-System said ithad reversed the flow to send back 4 million cubic metres perday, the equivalent of 1.5 billion annually - a modest volumecompared with Ukraine's need for more than 50 billion.
Moscow has nearly doubled the price it charges Kiev thisyear, and President Vladimir Putin has threatened to haltsupplies if Kiev does not repay more than $2 billion it owes toGazprom. Putin has also warned EU leaders that this coulddisrupt their supplies that flow across Ukraine.
Ukrainian state energy company Naftogaz said it was ready topay in full for imported gas from Russia at $268.5 per 1,000cubic metres, rather than the $485 Moscow has demanded, which ismore than it charges rich Western countries for its gas.
Despite the bad east-west climate, energy giant BP said its Russian business was unaffected by sanctions the UnitedStates and EU have imposed on people close to Putin. BP owns a19.75 percent stake in Kremlin-controlled Rosneft,which became the world's top listed oil producer last year.
(Additional reporting by Serhiy Karazy and Conor Humphries inKiev; Alessandra Prentice and Alexei Anishchuk in Moscow, TomGrove in Slaviansk, Ben Blanchard in Beijing, Adrian Croft inLuxembourg; Tom Miles and Stephanie Nebehay in Geneva; Writingby Giles Elgood; Editing by Peter Graff)
