North Korea's military personnel parade with a portrait of North Korea's late leader Kim Il-sung in central Pyongyang April 25, 2007. REUTERS/Korea News Service

SEOUL (Reuters) - North Korea conducted a nuclear test on Monday, South Korea’s Yonhap news agency quoted a ruling party official as saying.

YTN Television quoted the South Korean weather agency as saying it detected a tremor indicating a test at 0054 GMT (8:54 p.m. EDT).

South Korean President Lee Myung-bak had called an emergency meeting of cabinet ministers over the test, Yonhap said.

North Korea had recently said it would again test a nuclear device -- its first was in October 2006 -- in reaction to tightened international sanctions after it fired a long-range rocket in April.

News of the test hit South Korean financial markets, sending the main KOSPI share index down four percent in late morning trade, while the won dropped more than 1 percent against the dollar.