OSCE observers said Monday that Bulgaria's elections had overall been conducted properly but denounced "serious violations" such as the buying of votes in the run up to the polls.
The vote on Sunday was "held in a competitive environment, fundamental freedoms were respected, and the administration ... was well managed," a Organisation for Security and Cooperation in Europe statement said.
It added, however, that the campaign "was overshadowed by a number of incidents that diminished trust in state institutions and the process was negatively affected by pervasive allegations of vote-buying."
Miklos Haraszti, the head of the OSCE mission, the largest to Bulgaria since 1990 amid fears of irregularities in the former communist country, was much more critical in a news conference in Sofia on Monday.
"There were serious violations during the campaign," he said.
"Vote-buying was not stopped. It is difficult to understand why it is so difficult to stop it," he added as prosecutors probed some 60 cases of vote-buying especially among the country's poor Roma minority.
On Saturday opposition politicians reacted with uproar after authorities discovered 350,000 unaccounted-for ballot papers at a printing firm whose owner is reportedly close to ex-premier Boyko Borisov's GERB party.
Socialist party leader Sergey Stanishev said the discovery was "preparation for the total falsification of the elections," calling it a "scandal unseen in Bulgaria so far."
Allegations about illegal wiretapping by the outgoing cabinet also added to the poisonous atmosphere of the campaign, with some parties using "inflammatory and xenophobic rhetoric," the OSCE observers noted.
Mudslinging and bickering between politicians managed to completely steal the attention from people's grinding social problems just three months after massive and sometimes violent anti-poverty and corruption street tensions ousted the government.
"We were shocked by the alienation between citizens and institutions," Andreas Gross, head of the delegation from the Parliamentary Assembly of the Council of Europe, said.
"The lack of public confidence in the electoral process and the alienation of too many Bulgarians from their public institutions remains a matter of concern," he added.
"You cannot speak of generally fair elections. Money had too much to play. The fairness also means that people are not afraid. Much too many people have been afraid... or under pressure," Gross said.
"In this sense the legitimacy of the parliament is damaged," he added.
Five opposition parties -- excluding GERB -- also commissioned an independent vote count by an Austrian agency, although its findings broadly chimed with the official results.
Three months after mass protests forced his government's resignation, Borisov's GERB came first in the election, but well short of a majority and analysts predict he will fail to form a coalition.