"A humanitarian disaster is brewing in the besieged towns -- there is already a lack of medicines and there are starting to be disruptions of food supplies," the Russian foreign ministry said in a Monday statement.

Last week, Kiev launched an operation in Ukraine's Russian-speaking east in a bid to root out the pro-Moscow demonstrations.

Ukrainian troops on Monday were fighting rebels in the town of Slavyansk and had raided checkpoints in the nearby town of Kramatorsk to eradicate anti-government protesters who are holding more than a dozen towns.

The Russian foreign ministry said Ukraine was carrying out a "criminal operation" using "punitive methods" to target peaceful civilians and accused it of unleashing "terror against its own people."

Moscow urged Kiev to sit down at the negotiating table and "start a normal dialogue."

RA/NJF