The decision on who will become North Korea's next leader may not be final despite reports that Kim Jong Il has tapped his youngest son to succeed him, South Korea's defense chief said.

Who will take over as ruler of nuclear-armed North Korea after Kim has been the focus of intense speculation since the 67-year-old reportedly suffered a stroke last August.

South Korea's spy agency told lawmakers that Pyongyang notified its diplomatic missions and government agencies overseas that 26-year-old Kim Jong Un, the youngest of Kim's three sons, will inherit the leadership of the communist nation.

But Defense Minister Lee Sang-hee told the National Assembly on Tuesday that intelligence suggests a final decision has not been made. He did not elaborate.

His comments added to the murky succession drama in the reclusive country. The conflicting assessments come amid tensions over the North's May 25 nuclear test and signs that the regime is preparing to test-fire missiles in violation of U.N. Security Council resolutions.

Pyongyang has issued a no-sail zone through July 10 in waters off its east coast for "military drills."

Kim Jong Il has controlled the impoverished nation of 24 million with absolute authority since his father's death in 1994. Regional powers fear instability and a power struggle if he dies without naming a successor. North Korea has denied Kim was ever ill, but he appeared gaunt in an April appearance at parliament.

Lee told lawmakers that South Korea's military was keeping a close watch on Kim's health amid possible signs his condition has worsened.

Kim visited a semiconductor materials factory and the country's academy of sciences in the east coast city of Hamhung, the North's official Korean Central News Agency said Wednesday.

Lee also said it's clear that the North — which conducted two underground nuclear tests in 2006 and in May this year — was pursuing an uranium enrichment program, which can be more easily hidden than a plutonium-producing reactor.

Meanwhile, a U.S. delegation headed by Philip Goldberg left Tuesday for Beijing to discuss U.N. sanctions slapped on North Korea for a nuclear test last month, the State Department said. Goldberg, a former ambassador, is in charge of coordinating the sanctions' implementation.

China's cooperation in enforcing sanctions against its neighbor is seen as crucial to increasing pressure meant to push the North back to nuclear disarmament talks.

The new resolution seeks to clamp down on North Korea's trading of banned arms and weapons-related material by requiring U.N. member states to request inspections of ships suspected of carrying prohibited cargo.

In Washington, the U.S. Treasury Department on Tuesday imposed financial sanctions on Hong Kong Electronics, a company located in Kish Island, Iran, that is accused of involvement in North Korea's missile proliferation network.

The action means that any bank accounts or other financial assets found in the U.S. belonging to the company must be frozen. Americans also are prohibited from doing business with the firm.

It is the latest move by the U.S. to keep pressure on Pyongyang, whose nuclear ambitions have ratcheted up global tensions.

U.S. officials also said Tuesday that a North Korean ship — the first vessel monitored under the U.N. sanctions — had turned around and was headed back toward the north where it came from.

The freighter had been tracked for more than a week by U.S. Navy vessels on suspicion of carrying illegal weapons.

The ship was initially believed to be heading toward Myanmar. The move came after Myanmar's authorities told the North Korean ambassador they wouldn't allow the Kang Nam 1 to dock if it was carrying weapons or other banned materials, a Radio Free Asia report said.