Powerful radio emission is found in a small fraction of active galactic nuclei (AGN) and is associated with the presence of outflows of relativistic plasma produced in the innermost region. When the jet axis is aligned with our line of sight, the emission is characterized by strong variability across the entire electromagnetic spectrum, high polarization level, and presence of superluminal jet components. An intriguing aspect still unclear is the connection between the regions responsible for the emission at the various wavelengths, particularly in radio and gamma-ray bands.
In this contribution I will discuss results from multiwavelength observations of the flaring blazars PKS 1510-089 (z=0.361) and TXS 0536+145 (z=2.69). Since 2011, PKS 1510-089 has undergone to an extraordinary active phase in both radio and gamma rays, with an exceptional flaring episode in October 2011. On the other hand, TXS 0536+145 is the most luminous and distant flaring blazar yet detected by Fermi-LAT. I will investigate the possible connection between high-energy and low-energy bands by comparing the gamma-ray light curves collected by Fermi-LAT with those derived in the radio, by means of single-dish telescope monitoring campaigns, and optical bands. Very Long Baseline Interferometry observations with VERA, EVN and VLBA will be presented to constrain the ejection of new superluminal components on parsec-scale close in time with high-energy flares.