By Laura
Smith-Spark, Ben Brumfield and Victoria Butenko, CNN
April 25, 2014 -- Updated 0344 GMT (1144 HKT)
CNN
Kiev,
Ukraine (CNN) -- Tensions in
Ukraine escalated sharply
Thursday, with Russia
embarking on new military drills near the border after Ukrainian forces said
they killed five pro-Russian militants.
Ukraine's Interior Ministry said Ukrainian
forces killed the militants during operations to take down pro-Russian
activists' roadblocks around the southeastern city of Slavyansk.
The Russian
response was swift.
Russian
President Vladimir Putin said "if the Kiev regime has started to use the army
against the population inside the country, it, beyond any doubt, is a very
serious crime."