North Korea's economy grew 3.9 percent last year, the fastest pace in more than a decade, South Korea's central bank said Friday, despite tough UN sanctions over Pyongyang's nuclear and missile programs.

The estimated expansion of the gross domestic product represents a sharp turnaround from 2015 when the economy of one of the world's most isolated countries shrank 1.1 percent due mainly to a drought.

Last year's growth is the highest since 1999 when North Korea's economy expanded 6.1 percent, according to the Bank of Korea. 

North Korea's economy expanded 1.2 percent on average between 2012 and 2016, a sign that its economy is mired in low growth.

There are no indications that the North's economy has suddenly improved since late 2011 when North Korean leader Kim Jong-un took power on the sudden death of his father and long-time leader Kim Jong-il, an official said.

During late Kim's 17-year rule, the North's economy grew just 0.2 percent on average.

"North Korea's economic structure is very fragile and is not really set up for high growth," the official spoke on the condition of anonymity.

The BOK estimated North Korea's gross national income stood at 36.4 trillion won ($32.4 billion) in 2016. South Korea's per-capita GNI stood at 31.98 million won, which is 22.1 times larger than the North's 1.46 million won.

Daniel Pinkston, a Korea expert at Troy University in Seoul, said there seems to be some improvement in North Korea's economy, though he said it is always hard to trust the figures.

As North Korea does not release its official economic data, South Korea estimates North Korea's annual economic performance since 1991 based on information provided by South Korea's spy agency and other relevant organizations.

Related to last year's growth, the central bank said North Korea's mining industry grew 8.4 percent, the highest since 1999 when it expanded 14.2 percent.

North Korea's trade volume came to $6.55 billion in 2016, up 4.7 percent from a year earlier, the BOK said. The increase came despite tightened UN sanctions imposed on North Korea over its repeated nuclear tests and its long-range rocket launches.

The sanctions call for, among other things, a ban on the country's exports of coal and other mineral resources to cut off North Korea's access to hard currency.

Still, the provision will not apply if transactions are determined to be exclusively for livelihood purposes and unrelated to generating revenue for North Korea's nuclear or ballistic missile programs or other activities prohibited by previous UN resolutions.

China accounts for nearly 90 percent of North Korea's foreign trade, and mineral resources are a key part of their bilateral trade. (Yonhap)