KIEV, Ukraine (AP) -- The mayor of Ukraine's second-largest city was shot in the back Monday and pro-Russia insurgents seized yet another government building as tensions rose in eastern Ukraine ahead of a new round of U.S. sanctions.

Armed insurgents tacitly backed by Moscow are seeking more autonomy in the region. Ukraine's acting government and the West have accused Russia of orchestrating the unrest, which they fear Moscow could use as a pretext for an invasion. Last month, Russia annexed Crimea weeks after seizing control of the Black Sea peninsula.

In a bid to ratchet up the pressure on Russian President Vladimir Putin, President Barack Obama has promised to levy new sanctions on Russian individuals and companies in retaliation for Moscow's alleged provocations in eastern Ukraine.

Hennady Kernes, the mayor of Kharkiv, was shot in the back Monday morning, his office said. Kernes was said to be undergoing surgery and ``doctors are fighting for his life,'' according to the city hall.

Kharkiv city hall spokesman Yuri Sydorenko told the Interfax news agency that Kernes was shot while cycling along a road on the outskirts of the city.

Officials have not commented on who could be behind the attack.

Kernes was a staunch opponent of the pro-West Maidan movement that toppled President Viktor Yanukovych in February and was widely viewed as the organizer of activists sent to Kiev from eastern Ukraine to harass those demonstrators.

But he has since softened his stance toward the new Kiev government.  At a meeting of eastern Ukrainian leaders and acting Prime Minister Arseniy Yatsenyuk earlier this month, Kernes insisted he does not support the pro-Russia insurgents and backed a united Ukraine.

Kharkiv is in eastern Ukraine, where pro-Russia gunmen have seized government buildings and police stations, set up roadblocks or staged protests to demand greater autonomy or outright annexation by Russia. But unlike the neighboring Donetsk region, Kharkiv has been largely unaffected by the insurgency. Its regional administration building was briefly seized earlier this month but promptly cleared of pro-Russian protesters.

On Monday, masked militants with automatic weapons seized another city hall building and a police station, this time in Kostyantynivka, 160 kilometers (100 miles) from the Russian border.  The city is 35 kilometers (22 miles) south of Slovyansk, a major city in eastern Ukraine that has been in insurgents' hands for more than three weeks now.

After the seizure, about 15 armed men guarded the city hall building. Some posed for pictures with residents while others distributed St. George's ribbons, the symbol of the pro-Russia movement.

On visit to the Philippines earlier Monday, Obama said the targets of the latest U.S. sanctions will include high-technology exports to Russia's defense industry. The full list, which is also expected to include wealthy allies of Putin, will be announced by officials in Washington later Monday.

The European Union is also planning more sanctions against Russia, with ambassadors from the bloc's 28 members meeting Monday in Brussels to add to the list of Russian officials who have been hit by asset freezes and travel bans.

Meanwhile, the increasingly ruthless pro-Russia insurgency is turning to an ominous new tactic: kidnapping. About 40 people are being held hostage in makeshift jails in Slovyansk _ including journalists, pro-Ukraine activists and seven military observers from the Organization of Security and Cooperation in Europe, Ukraine's Security Service said Monday.

The German government on Monday decried the seizure of the European military observers and called for their immediate release. Eight observers, including three German officers, were detained Friday on allegations they were spying for NATO. One Swedish officer among them was released Sunday.

Pro-Russia militants in camouflage and black balaclavas paraded some of the captive military observers before the media on Sunday. They also showed three Ukrainian security guards bloodied, blindfolded, stripped of their trousers and shoes, their arms bound with packing tape.

German captive Col. Axel Schneider spoke at Sunday's news conference _ under armed guard _ saying they were on an OSCE diplomatic mission and were not spies.