North Korea's crumbling economy is feeling the effects of sanctions for nuclear and ballistic missile activities, with foreign trade falling 10 percent in 2009 from the previous year, South Korea said on Monday.

The state-run Korea Trade-Investment Promotion Agency (KOTRA) said North Korea's trade, including commerce with South Korea, fell 9.7 percent to $5.09 billion last year from 2008.

Excluding trade with the South, foreign commerce feel 10.5 percent to $3.41 billion last year, KOTRA said in a statement.

It said trade with China, the North's sole supporter, amounted to about $2.7 billion.

The prospect of further sanctions as a result of the sinking of a South Korean naval vessel by a suspected North Korean torpedo in March would slow trade even more, KOTRA said.

North Korea's trade this year is seen shrinking further and depending more on China due to the U.N.'s continuous sanctions against the North and possibilities of further measures, KOTRA said.

North Korea does not announce its own trade data and KOTRA said it compiled the data from the agency's overseas offices.

Last week, Seoul released the findings of a report which concluded that a North Korean submarine had fired a torpedo that sank the Cheonan corvette, killing 46 sailors.

South Korea has repeatedly said it would not strike back at the North, aware that would frighten away investors already jittery about the escalating tension on the divided peninsula.

Washington has called for an international response, which could range from fresh U.N. Security Council sanctions on North Korea, although those might be opposed by China, to a statement of condemnation by the world body.

A range of international sanctions have been levied against North Korea in recent years for its missile and nuclear tests.

(Reporting by Cheon Jong-woo; Editing by Jeremy Laurence)