"The region is characterised by a vicious cycle in which a highly elitist and unaccountable political culture remains largely unchallenged because the very actors who can bring those in power to task are being systematically silenced," said Transparency International Asia-Pacific director Srirak Plipat.
The report comes days after India's Congress party, embroiled in a string of corruption scandals during its 10 years in power, was thrown out of office in national elections.
"As long as nobody brings the corrupt to justice, South Asia's leaders run the risk that future growth only benefits the powerful, doing nothing to help the half-billion South Asians who still live in poverty," said Plipat.
In many cases, South Asian watchdogs are deliberately weakened by their governments, while officials also use agencies to settle scores with political opponents or to protect powerful backers, Transparency International said.
With the exception of Sri Lanka, the countries surveyed have legislation to protect the public's right to information -- but citizens are often unable to use the laws effectively because of official reluctance to respond to requests, the report said.
The study also found that whistle-blowers confront huge dangers when they attempt to expose corruption, with most South Asian countries lacking laws to protect them. Officials who try to expose wrongdoing face the risk of being transferred or removed from office.
South Asia is considered one of the world's most graft-ridden regions, according to the watchdog, with high-profile politicians embroiled in huge corruption cases and many citizens complaining of being forced to pay bribes for essential services.
