Twenty Scud missiles fired by Yemeni rebels into Saudi Arabia in recent months were bought from North Korea, a South Korean intelligence official told Yonhap News on Wednesday. The official, who spoke on the condition of anonymity, did not give further details as to how South Korean intelligence had reached that conclusion, though officials in South Korea and the U.S. have long been aware that North Korea sold missiles to other nations.

In an effort to earn hard currency in a struggling economy, North Korea has reportedly sold missiles to nations in the Middle East -- such as Iran, Syria and Pakistan, and allegedly to Hamas, which the U.S. has designated as a terrorist organization. North Korea is so well-known for selling missiles to foreign powers that some in intelligence circles refer to the country as "Missiles R Us," according to professor Graham T. Allison Jr., who specializes in international nuclear politics at Harvard University's John F. Kennedy School of Government in Cambridge, Massachusetts.

News of the missiles' origin came amid heightened violence in Yemen. The Houthi rebels, a Shiite ethnic group in Yemen, overthrew the government in Sanaa in January, causing the entire leadership to flee. A civil war between Houthi rebels and Yemeni government loyalists has ensued.

GettyImages-482332102 A fighter loyal to Yemen's exiled government walked with crutches in Aden, Yemen, on July 30, 2015. The city has been shelled by Houthi rebels and hit with Saudi airstrikes in recent months, following a Yemeni rebellion that overthrew the government and plunged the nation into civil war. Photo: Agence France-Presse/Getty Images

In March a coalition led by neighboring Saudi Arabia, a nation still loyal to the deposed government, conducted airstrikes on Yemen. Fighting between the Houthis and the Saudis has raged in recent months, with the death toll in early July estimated at 3,000 people, with 20 million more in need of aid

The Yemeni rebels have not been as successful as the Saudis in their airstrikes. On June 6, Saudi forces shot down a missile fired from Yemen and have brought down many more since. The move was still seen as an important escalation in the war as well as a message to Saudi Arabia that the Houthis had missile capacity.