South Korean military officials said Monday they couldn't immediately confirm the report. Yonhap cited unidentified government officials as saying the missile test occurred off the east coast.
North Korea is urging its people to rally behind Kim Jong Il's young son and heir-apparent Kim Jong Un. The world is watching warily for signs of instability in a nation pursuing nuclear weapons.
South Korea has put its military on high alert against the North's 1.2 million-strong armed forces. President Barack Obama agreed by phone with South Korean President Lee Myung-bak to closely monitor developments.