Since year 2017, radio telescopes of Ventspils International Radio Astronomy Centre (VIRAC)
are used to study intra-day and inter-day variability of various types of active galactic nuclei
(AGN). These studies are based on a generalization of the results of a 40-year monitoring of
extragalactic radio sources flux conducted by Michigan Radio Astronomy Observatory in the
USA using wavelet and Fourier analysis performed at Odessa Observatory of the Radio
Astronomy Institute of the National Academy of Sciences (NAS) of Ukraine. On this basis, a
catalogue for the properties of the variability of extragalactic radio sources was created. The
extension of the temporal spectrum of flux changes to inter-diurnal and diurnal scales is carried
out with the help of VIRAC radio telescopes RT-32 and RT-16 respectively with 32- and 16-meter
antennas. The intra-day variability of the calibration source 3C295 (Type 2 Seyfert Galaxy) is
detected and preliminary results presented in the paper for discussion. Several other radio sources
(3C 273, 3C 454.3, OJ 287, BL Lac) are suspected to have variability of such type and are
scheduled for monitoring observations as well. The paper discusses possibility of observing these
promising objects during VLBI sessions by EVN and parallel long-term total flux monitoring with
VIRAC antennas. The temporal changes in flux linked with VLBI maps opens opportunity to
determine the nature of the physical processes that form fast flux changes of various types of
active galactic nuclei.