On a street in ousted President Viktor Yanukovych's political stronghold, Donetsk, stands the imposing headquarters of the Mako Group, a Ukrainian conglomerate spanning banking to construction.

The 20-story block is modern but designed in the style of the Stalin era and contains a hotel, restaurant, bank, and Mako's unmarked offices — all, according to residents, belonging to Yanukovych's eldest son, Oleksandr, 40. The business activities of the son, who trained as a dentist, have long been the object of scrutiny by critics of his father.

Two opposition research groups, PEPWatch and Anticorruption Action Centre, say on yanukovych.info, a website they jointly run, that Oleksandr Yanukovych's assets have risen by 7,285 percent in three years. These were valued at $510 million by Forbes-Ukraine last year.