Pro-Russia Militants Killed in Ukraine Offensive

Thirty pro-Russian insurgents have been killed in Ukraine's latest push to remove anti-government forces from the east.

Ukraine's interior minister said four government troops also died and another 20 were injured during fighting in Slovyansk. The deadly gun battles took place at several positions around the city.

"In recent days, the anti-terrorist operation has aimed to destroy heavily armed militants," Valentyn Nalyvaichenko, the head of Ukraine's Security Service, said.

"Around 30 militants were killed," he continued. "Also, their groups around Slovyansk were eliminated. We tried to avoid having armed forces enter in those cities where many peaceful citizens live."

Although Ukrainian troops are tightening security around some major eastern cities, pro-Russian militias are advancing in other areas, surrounding a major Interior Ministry base Tuesday afternoon.

"We got information that this base was going to be attacked and the weapons taken," one pro-Russian insurgent said. "We do not want those weapons to be used against us."

Dozens of government buildings and police stations have been seized by insurgents over the past several weeks.

Ukraine authorities and the West blame Moscow for the continued unrest. They say it's an attempt to derail Ukraine's May 25 presidential election.

"The Russians, Vladimir Putin, today would like this election not to take place in order to continue to exert pressure. It's up to us to convince him," French President Francois Hollande said.

But Russia questions the timing of the elections.

"Scheduling elections in times when the army is used against parts of the population is not conventional," Russian Foreign Minister Sergey Lavrov said. "This is not Afghanistan."

Meanwhile, CEOs of several major U.S. companies are complying with a request by the Obama administration to boycott an economic summit in Russia later this month, The New York Times reports.

"Obviously, companies will have to make their own decisions, but we believe that the most senior business executives traveling to Russia to make high-profile appearances with Russian government officials at events such as this would send an inappropriate message," the Times quoted White House spokeswoman Laura Lucas Magnuson.

The goal of the boycott is to isolate the Russian government over its violation of Ukrainian sovereignty.

The U.S. government is also planning to punish Russia using one of its most feared economic weapons: the Internal Revenue Service.

Top Russian officials have already been targeted with sanctions. Now the plan is to enforce an existing anti-tax-evasion law against Russian financial institutions and investors.

Some believe this step could prove even more costly than sanctions.

"If sanctions are going to be limited to certain targeted individuals and banks, where this applies to everybody in the market, yes, I think this could potentially be worse than sanctions for the Russians," said Brian L. Zimbler, from the Moscow office of the international law firm Morgan Lewis.

The move would target Russian banks with a 30 percent tax on investments they make inside the United States, including stocks and bonds.

"It's a huge deal," Mark E. Matthews, a former IRS deputy commissioner, said. "It would throw enormous uncertainty into the Russian banking community."