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We report long-term observations of H2O and OH maser emission sources at wavelengths of 1.35 and 18 cm associated with star-forming regions. Strong quasi-periodic flares of maser emission have been observed. Several sources (in particular, G25.65+1.05, IRAS 16293−2422, Cep A) have displayed strong flares in the H2O line, when their peak flux density raised by a few orders of magnitude above the quiet state. Possible causes of this are discussed.

In 2017-18 the source of outstanding H2O maser bursts G25.65+1.05 have been intensively studied with a wide range of baselines - from compact array (JVLA) and ground VLBI (EVN, VLBA, KaVA) to space VLBI (RadioAstron mission supported by VLBA and EVN telescopes) - the report gives a brief summary of these observations.

H$_2$O masers associated with the massive star formation region W49N were observed in frames of the Space-VLBI project RadioAstron. Ultra-compact structures in the masers were detected on space-ground baselines up to 9.6 Earth diameters. The flux density of ultra-compact features does not exceed a percent of the single dish flux density. Some results of the data processing for three observing sessions performed in 2014-2015 are presented. The lower limit of minimal brightness temperatures and estimates of angular sizes of the brightest features corresponding to the ultra-compact maser spots of the W49N complex are obtained.