At least seven bomb blasts in little more than a month in Ukraine's second-largest city, Kharkiv, have stirred fears among residents and the government in Kiev that Russia-backed rebels are trying to destabilize the militarily strategic region.
International monitors from the Organization for Security and Cooperation in Europe have examined the areas of attack and noted rising tensions in the city in their daily reports on unrest in eastern Ukraine.
In the most destructive of the blasts, which Kharkiv regional prosecutors are investigating as an act of terrorism, 11 people were wounded when a bomb went off in the popular Stina rock pub in the city center Nov. 9.
In addition to the bombing at the pub, which had been active in raising money for Ukrainian forces battling pro-Russia separatists in two neighboring eastern Ukrainian regions, the targets have included a hospital for security forces, a military recruiting center and a national guard base where Dutch investigators were probing the wreckage of the July 17 Malaysia Airlines disaster.
Kharkiv, a city of 1.4 million that is home to some of Ukraine's most important defense industries, was seized by a few dozen pro-Russia gunmen in the early days of the rebellion spurred by the overthrow of Kremlin-allied President Viktor Yanukovich in February. But a civic uprising and an influx of security forces from Kiev, the capital, deposed the occupiers within days. About half of them turned out to have come across the border from Russia to aid local militants opposed to the new national government, security officials have said.
Among the key industries based in Kharkiv city and the sprawling region that borders Russia are Khartron Industries, which produces missile guidance systems, the Malyshev tank factory and the Dzerzhinsky machine-building enterprise.
As the largest and most important government-controlled city in the turbulent east, Kharkiv has been used since August as a temporary morgue and forensic investigations center for the remains and wreckage recovered from separatist-held territory in the Donetsk region, where the Malaysia Boeing 777 crashed.
The disaster, in which all 298 on board perished, has been blamed by Kiev authorities and Western governments on the Moscow-backed insurgents who reportedly mistook the passenger plane for a Ukrainian military transport.
A bomb detonated outside the gates of a national guard base Dec. 2, near the area where the Dutch team was loading plane debris brought from the crash field for transport to the forensic investigations center in the Netherlands, Kiev media reported.
The head of the Security Service of Ukraine, Valentyn Nalyvaichenko, told reporters at a briefing last month that agents had thwarted a plot instigated by Russian special forces to bomb a convoy of Dutch government officials visiting Kharkiv. Authorities learned of the attack plan from a woman detained for questioning in the pub bombing, who Nalyvaichenko said provided "clear evidence" of Russian security agents training local militants for the planned attack.
Russian security forces were also said to be behind a plot to recruit Ukrainian pilots to the side of the pro-Russia separatists and pay them as much as $300,000 to hijack Ukrainian military aircraft from a base in the Mykolaiv region, the Ukrinform news agency reported in late November, citing security sources.
Fighting between the Moscow-backed separatists and Ukrainian government forces has slowed in recent weeks, partly because of efforts to observe a cease-fire and resume peace talks and also because winter weather is hampering both sides' efforts to wage offensives.
More than 4,300 people have died since the conflict in eastern Ukraine broke out after Russia's annexation of the Crimea area, home to its Black Sea naval fleet and other vital military venues it had leased from Ukraine since the 1991 breakup of the Soviet Union.