IZYUM, Ukraine (AP) -- Busloads of Ukrainian troops and a handful of tanks set up Tuesday outside an eastern city controlled by armed pro-Russian militiamen as the country's acting president announced an "anti-terrorist operation" to root out the separatists.
Much of the focus Tuesday was around the eastern city of Slovyansk, 160 kilometers (100 miles) from the Russian border, which has come under the increasing control of the gunmen who seized it last weekend.
An Associated Press reporter saw at least 14 armored personnel carriers with Ukrainian flags, one helicopter and military trucks parked 40 kilometers (24 miles) north of the city. Other heavy military equipment appeared nearby, along with at least seven busloads of government troops in black military fatigues.
"We are awaiting the order to move on Sloyvansk," said one soldier, who gave only his first name, Taras.
Two of the helicopters loaded with troops later took off and headed toward Slovyansk.
Russia's state RIA Novosti news agency reported that Ukrainian army troops wounded two pro-Russian militiamen Tuesday during a skirmish near a small airport in Kramatorsk, not far from Slovyansk. The report could not independently be confirmed.
RIA Novosti said the troops drove to the airport n an armored personnel carrier, started talking to the gunmen who control the site and a skirmish broke out. It did not elaborate.
The armed pro-Russian militias are occupying government, police and other administrative buildings in at least nine cities in Ukraine's Russian-speaking east of the country, demanding broader autonomy and closer ties with Russia. The central government has so far been unable to rein in the insurgents, and many local security forces have switched to their side.
Prior to the reported government offensive, roads into Slovyansk were dotted Tuesday with militia checkpoints, at least one with a Russian flag. Another bore a sign "If we don't do it, nobody will."
And the threat the Ukrainian military posed to the highly organized, pro-Russian insurgents was unclear. One video posted online late Monday showed a hapless Ukrainian tank stuck in the mud in a field reportedly outside Slovyansk. Residents chased it on foot, shouting "Who are you going to fire at?"
The government in Kiev, the capital, for days has been promising to deploy troops to root out the armed separatists, but until Tuesday there was little visible action.
Russia itself still has tens of thousands of troops massed along Ukraine's eastern border. Western governments accuse Moscow of fueling the unrest in eastern Ukraine and worry that any bloodshed could be used as a pretext for a Russian invasion, in a repeat of events in Crimea a few weeks ago.
Russia annexed Ukraine's Crimean Peninsula after seizing it last month following the ouster of Ukraine's pro-Russian president in February.
Backing up its claims that Russia was behind the unrest, Ukraine's security services on Tuesday identified one of the leaders of the pro-Russian operation in Slovyansk as a Russian foreign intelligence agent named Igor Strelkov. It said Strelkov also coordinated Russian troops in Crimea during the seizure of military facilities there.
In a phone call Monday, Russian President Vladimir Putin urged President Barack Obama to discourage the Ukrainian government from using force against protesters in the country's east.
A wave of sit-ins, meanwhile, has hit the eastern city of Horlivka, where a police station was seized Monday by unidentified gunmen. Outside the station, a sign pinned to a barricade of tires listed items required by protesters, including blankets, drinking water and tape to cover up windows smashed during the storming.
Anatoly Zhurov, a 53-year-old Horlivka resident, said the insurgents' goal was to resist the government in Kiev.
Elsewhere, the Interior Ministry said a police station in the eastern city of Kramatorsk that had been seized by pro-Russian gunmen was "liberated" Tuesday.
Ukraine's acting president, Oleksandr Turchynov, gave few details of the "anti-terrorist operation" to the parliament in Kiev, saying only that it would be conducted in a "responsible and balanced" manner. He blamed Russia for sponsoring the camouflage-wearing insurgents, who are often armed and move with a precision unlikely for local militia.
"(Russia wants) the whole south and east of Ukraine to be engulfed by fire," Turchynov said, adding the government operation aimed to "defend the citizens of Ukraine, to stop terror, stop crime and stop attempts to tear our country into pieces."
Russia strongly warned Kiev against using force against the pro-Russian protesters, saying that could prompt Moscow to walk out of Thursday's international conference on Ukraine in Geneva.
"You can't send in tanks and at the same time hold talks. The use of force would sabotage the opportunity offered by the four-party negotiations in Geneva," Russian Foreign Minister Sergey Lavrov said Tuesday.
"Ukraine is on the verge of a civil war, it's horrible," Russian Prime Minister Dmitry Medvedev said in Moscow, adding that Ukraine's government must talks with all segments of its population
In a sign that Ukraine's economic situation is becoming even more dire, its central bank increased its benchmark interest rate by a whopping 7 percent to 14.5 percent.
Ukraine has relied on cheap gas supplies from Russia for years. Moscow raised the gas prices for Kiev in the past weeks, leaving Ukraine scrambling to pay the mounting gas bills as well as past bills that Putin now says adds up to over $35 billion.
In the wake of Moscow's threats to cut off energy supplies to Ukraine, the German utility company RWE AG said Tuesday it has started supplying gas to Ukraine via Poland and could sell it up to 10 billion cubic meters of natural gas a year. Ukraine consumes between 52 and 55 billion cubic meters of gas a year.
In Kiev, two pro-Russian politicians were attacked by pro-Western activists as tensions mounted over unrest in the east.
Oleh Tsaryov, a pro-Russian lawmaker and a candidate in the May 25 presidential elections, was beaten by dozens of enraged activists early Tuesday as he was leaving a television studio. The activists pelted him with eggs, shouted insults and then assaulted him.
The Ukrainian Prosecutor General's Office said it has opened a probe into the attack -- as well as a criminal case against Tsaryov's calls to "encroach on Ukraine's territorial integrity." The lawmaker has met with pro-Russian protesters in Donetsk.
Another Russian-leaning politician and presidential hopeful, Mikhaylo Dobkin, was hit by green disinfectant and flour late Monday.
Moscow has accused the Kiev authorities of condoning such radicalism and says attacks against pro-Russian candidates show that the presidential election will not be fair or democratic.
Peter Leonard in Donetsk, Maria Danilova and Nataliya Vasilyeva in Kiev, and Christopher Bodeen in Beijing contributed to this report.