Roads into Slovyansk, a city some 160 kilometers (100 miles) east of Russia that has come under ever more secure control of the gunmen since Saturday, were dotted with checkpoints. One at the entrance into town was waving a Russian flag. Another bore a sign reading "If we don't do it, nobody will."
Despite mounting fears of an imminent assault by Ukrainian government troops, the town appeared calm at midday.
In Kiev, Ukraine's acting president, Oleksandr Turchynov, announced an "anti-terrorist operation" to root out the "separatists," but it was unclear how that measure differed from the one announced Monday, which resulted in no visible action.
The insurgents, many of them armed, continued occupying government, police and other administrative buildings in nearly nine cities in the country'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, as many of the local security forces have switched to their side.
The unrest comes a month after Russia annexed Ukraine's Crimean Peninsula, after a pro-Russian president was ousted after three months of pro-Western protests.
The city of Horlivka, not far from the Russian border, where the local police station was seized by unidentified gunmen on Monday, has been turned into the latest of a wave of sit-ins across eastern Ukraine, where at least nine cities appeared in control of the insurgents.
Outside the police station, a sign pinned to the wall of tires listed items required by protesters, including blankets, drinking water and tape to cover up windows smashed during the storming of the building.
Anatoly Zhurov, a 53-year old Horlivka resident participating in the defense of the site, said their goal was to resist the government in Kiev.
Turchynov, speaking to parliament, gave few details of the "anti-terrorist operation," saying only that it would be conducted in a "responsible and balanced" manner.
"The plans of the Russian Federation were and remain brutal. They want not only for Donbass (Donetsk region), but for the whole south and east of Ukraine to be engulfed by fire," Turchynov said. The aim of the operation is to "defend the citizens of Ukraine, to stop terror, stop crime and stop attempts to tear our country into pieces," he said.
Russia strongly warned Kiev against using force against the pro-Russian protesters, saying Moscow could walk out of an international conference devoted to the Ukrainian crisis scheduled for Thursday.
"If force is used in southeastern Ukraine, chances of holding this meeting in Geneva would be undermined," Russian Foreign Minister Sergey Lavrov said at a press conference Tuesday after talks with Chinese Foreign Minister Wang Yi.
In a sign the economic situation is becoming ever more difficult, Ukraine's central bank increased its benchmark interest rate by a whopping 7 percent to 14.5 percent.
The move aims to contain the risk of inflation by supporting the currency, which has been falling to record lows in recent days. A dropping currency fuels inflation by boosting the cost of imports.
However, hiking interest rates can cause collateral damage to the economy by making loans and mortgages more expensive to residents and businesses.
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 in the early hours of Tuesday as he was leaving a television studio. The activists pelted him with eggs, shouted insults and then assaulted him.
Tsaryov's press service said in a statement that he was "brutally beaten."
Another Russian-leaning politician and presidential hopeful, Mikhaylo Dobkin, was sprayed with a green disinfectant and had flour thrown at him late Monday.
Moscow accused Kiev authorities of condoning such radicalism and said the attacks proved that presidential elections will not be fair or democratic.
Peter Leonard in Donetsk, Maria Danilova and Nataliya Vasilyeva in Kiev contributed to this report.