North Korea's trade volume sank 18 percent last year from a year earlier, ending five years of straight growth, due largely to a drop in the prices of its key trading items such as coal and overall shipments, a South Korean trade agency said Wednesday.

The North's overall trade volume came to $6.25 billion in 2015, compared with $7.61 billion the previous year, according to the state-run Korea Trade-Investment Promotion Agency.

The reclusive country's outbound shipments fell 15 percent on-year to reach $2.7 billion, while imports also dropped 30 percent to $3.55 billion over the cited period, the data compiled by the agency showed.

Consequently, the communist state's trade deficit reached $850 million last year, narrowing 33 percent from the previous year.

The North's trade volume has been on a rising path since 2009 reaching an all-time high of $7.61 billion in 2014.

But a drop in prices of key trade items such as coal, coupled with a slowdown in China -- its strongest ally -- led to a decline in overall trade volume, KOTRA said.

Bilateral trade volume between North Korea and China came to $5.71 billion last year, down 16.8 percent from a year earlier.

The figure accounted for 91.3 percent of the North's overall trade in 2015, slightly higher than the previous year's 90.1 percent.

North Korea's dependence on China for trade has been increasing steadily since 2005 when its trade volume with China exceeded 50 percent of its overall trade.

Russia, another North Korean ally, was the country's second-largest trading partner in 2015, with bilateral trade volume reaching $84 million, followed by India with $77 million and Thailand with $50 million.

The North's largest export item was fuel such as coal, the shipments of which dropped 8.1 percent to $1.08 billion. The item accounted for 40.2 percent of its overall exports, the data showed.

Exports of clothing rose 5.5 percent on-year to $800 million, with its portion in the North's entire export rising to 29.7 percent from 24.1 percent in 2014. (Yonhap)