North Korea's political instability took a turn for the worse in 2013 from a year earlier, the World Bank said Tuesday, apparently due to the execution of its leader's uncle.

The bank's annual World Governance Indicators (WGI) data showed the aggregate indicator of "political stability and absence of violence (PV)" for the communist nation dropped to minus 0.53 in 2013 from minus 0.11 a year earlier.

It marks the lowest PV figure for North Korea since the bank launched the WGI program in 1996. The WGI is a set of composite governance indicators based on 32 underlying data sources, with scores ranging from minus 2.5 to plus 2.5, according to the bank.

It is designed to assess the level of their governance in six fields -- voice and accountability, political stability and absence of violence, government effectiveness, regulatory quality, rule of law and control of corruption.

The World Bank didn't give reasons for the drop, but it is viewed as attributable to the surprise purging of Jang Song-thaek, the once powerful uncle of the North's young leader Kim Jong-un, in late 2012.

North Korea's PV index started with minus 0.51 in 1996, two years after the death of its founding leader Kim Il-sung. But it improved to plus 0.54 in 2008. It dropped to minus 0.38 in 2010 amid reports of then North Korean leader Kim Jong-il's health problem.

It improved again in 2011 and 2012 after the current leader Kim Jong-un took power following his father's death.

Political stability in North Korea has drawn keen international attention again over the past weeks amid growing speculation about why Kim Jong-un is not making any public appearances.

Kim, known to be in his early 30s, was absent from the second session of the 13th Supreme People's Assembly last week. There has been no report by the North's state media on his public activity since almost a month ago.

It has spawned speculation that Kim is possibly sick or there has been an unexpected political incident in the secretive country. (Yonhap)