Amnesty International on Thursday accused South Korea of systematically abusing a 65-year-old security law in order to stifle debate and silence political opposition in Asia's fourth-largest economy, AFP reports.
In a 40-page report the rights watchdog documented a "dramatic increase" in the use of the National Security Law (NSL) under the administration of President Lee Myung-Bak, who took office in 2008.
Since 2008, the authorities have increasingly used vaguely worded clauses of the NSL to arbitrarily target people or organisations perceived to oppose government policies, especially on North Korea, Amnesty said.
"The NSL is being used as a smoke screen to hound critics of the government, with serious consequences for those targeted," Rajiv Narayan, Amnesty's East Asia Researcher, said in a statement.
The report cited figures from the National Prosecutors Office showing the number of new cases registered under the NSL had nearly doubled from 46 in 2008 to 90 in 2011.
The majority were booked on charges of posting allegedly pro-Pyongyang content online.
"No one is denying the right of South Korea to ensure the security of its citizens. But that is not what is being witnessed with the arbitrary and widening application of the NSL. Such abuse has to end," Narayan said.
The NSL was adopted in 1948 with the establishment of the Republic of Korea.
Its stated aim was to protect the fledgling South Korean government against espionage and other threats from a belligerent North Korea.
The United Nations has been calling for decades for the reform of the legislation, criticising its use to counter political dissent.
The Amnesty report highlighted what it described as an emerging trend for invoking the NSL against individuals and groups that had no tangible pro-North Korea stance.
In a recent case, a South Korean court handed down a 10-month suspended prison sentence to a 24-year-old photographer, Park Jeung-Geun, who re-tweeted postings from a North Korean Twitter account.
The release of the Amnesty report comes just weeks before South Koreans go to the polls to choose a replacement for Lee, who must stand down having served the one five-year term allowed by the constitution.
Kal Sang-Don, the director of Amnesty's Korean unit, said Lee's administration and the intelligence services had colluded in the "indiscriminate" application of the NSL.
Both took advantage of incidents of genuine North Korea aggression, such as the 2010 shelling of a border island, to invoke and then abuse the law, Kal said.
"As long as the national security law exists, intelligence authorities constantly try to prove the legitimacy of their presence," he added.
Amnesty said it had written to all the presidential candidates, urging them to abolish or fundamentally reform the NSL.