Support for Bulgaria's two largest parties - recent rulers GERB and opposition Bulgarian Socialist Party - has shrunk in March following the events that led to the resignation of GERB PM Boyko Borisov, according to an opinion survey.

The poll, conducted by the Bulgarian unit of Gallup International, also shows nationalists Ataka gaining ground, while the new party of ex-EU commissioner Meglena Kuneva, Bulgaria for Citizens, recording shrunken support.

The percentage of people who said they would vote for center-right GERB has fallen steadily from 23.8% in January to 22% in February and 19.7% in March, according to the poll, the results of which were published in the Pressa daily.

The situation with the Bulgarian Socialist Party is more interesting, as it recorded a rise of voter readiness from 19.7% in January to 22% in February, only to see support plummetting again to 18.6% in March.

February 20 then-PM Boyko Borisov surprisingly filed his resignation after a string of massive street protests against economic and social stagnation and political corruption in Bulgaria.

According to the Gallup survey, support for Meglena Kuneva's Bulgaria for Citizens has dropped from a steady 4.9% and 4.8% in the first two months to 3% in March, which is below the 4% election threshold.

In contrast, the support for the nationalist Ataka party has sharply risen from a mere 1.2% in January and February to 5% in March.

Apart from those four parties, the other party likely to enter Parliament after May 12 early elections is the party which comes third in support - the liberal Movement for Rights and Freedoms.

The Movement has however also been hit by the negative trend - from 7% and 7.3% in the first two months, to 5.2% in March.

According to the Gallup poll, the heirs to the rightist Blue Coalition - Democrats for Strong Bulgaria and Union of Democratic Forces - hover around a feeble support of 1% each for the first three months of 2013.