Bulgaria's president on Tuesday vetoed legislation demanded by Brussels aimed at tackling rampant corruption, saying it fails to protect whistleblowers.

Bulgaria, which took over the European Union's rotating presidency on January 1, is the poorest country in the bloc and according to watchdog Transparency International also the most corrupt.

Eleven years after joining the EU and despite being subject to a special EU monitoring system, no single high-ranking official has been jailed.

In a move towards reform, parliament approved the new law in late December with a view to merging several existing agencies into a single body to fight corruption.

It also broadened the list of high-level officials whose income, property and conflict-of-interest declarations would be subject to checks by the new body.

Parliamentarians however ruled out the possibility of lodging anonymous complaints against politicians, while also offering no protection from prosecution to whistleblowers.

President Rumen Radev, warning of the "risk for repressive action", said the proviso went against the Council of Europe's Civil Law Convention on Corruption protecting people who report graft.

Setting up the new structure may not be enough to solve such deeply rooted problems and the body may quickly be overburdened, Radev said.

He added that the fact that its five-member board is to be elected by parliament also created the risk of political meddling.

Radev's veto obliges parliament to re-examine the bill but lawmakers can also overrule his objections, forcing him to sign the law even if it remains unchanged.

Administrative and political corruption has become so endemic as to be perceived as normal, according to the Centre for the Study of Democracy, a Sofia-based think tank.

Corruption has drawn in judges, politicians and other officials to the point of "state capture" where government decision-making is effectively put in the hands of a powerful few, it said.