SEOUL, South Korea - North Korea pushed forward with preparations to test-fire more missiles in the wake of last week's nuclear test as leader Kim Jong Il moved to anoint his third son as heir to the world's first communist dynasty, reports and experts said Tuesday.

At least four missiles were spotted being readied at North Korean launch pads: a long-range missile on the west coast near China and three to four medium-range missiles on the east coast. U.S. military officials confirmed the preparations of a Taepodong-2 capable of striking the U.S., and the Yonhap news agency cited a legislator briefed by defense officials for the east coast launch.

North Korea was also strengthening its defenses and conducting amphibious assault exercises along its western shore - possible preparations for skirmishes at sea, reports said. South Korea deployed a guided-missile, high-speed boat to the area to stamp out any provocations, the navy said.

As tensions continued to escalate - with United Nations ambassadors discussing a new Security Council resolution in response to the nuclear test - the regime reportedly began paving the way for Kim's 26-year-old son, Jong Un, to eventually take over as leader of the nation of 24 million people.

A succession announcement went out after the May 25 underground nuclear test to top Workers' Party, military and government officials, South Korea's Dong-a Ilbo and Hankook Ilbo newspapers said Tuesday, and the North was already hailing the son as "our Commander Kim" in a new song being taught to the people, the Dong-a Ilbo said.

South Korea's National Intelligence Service said it cannot confirm the reports.

Analysts say the recent saber rattling is part of a campaign to build unity and support for the eventual successor to 67-year-old Kim Jong Il, who reportedly suffered a stroke last August.

After disappearing from the public eye for weeks last fall, Kim made his first state appearance in months at the delayed opening session of the country's new legislature April 12, grayer and thinner and limping slightly.

Kim was believed to want to name a successor by 2012 - the centenary of the birth of his father, North Korea founder Kim Il Sung - and the regime undertook a massive campaign last year to prepare the country for the 100th anniversary celebrations.

The April 5 launch of what North Korea claimed was a successful bid to send a communications satellite into space was believed part of the campaign, to show off the country's scientific advancements. But in an abrupt shift in plans, the regime stepped up the pace and in early May launched a "150-day battle" urging North Koreans to work harder to build up the country's economy.

"Before 2012, North Korea must convince the army and the public that Jong Un is the best successor," said Atsuhito Isozaki, assistant professor of North Korean politics at Tokyo's private Keio University. "To pave the way for Jong Un's leadership, it is highly likely that North Korea will turn recent nuclear and missile tests into his achievements."

Analyst Cheong Seong-chang of the Sejong Institute, a South Korean security think tank, noted that the "politically driven" campaign is set to end in early October, about the time of the anniversary of the founding of the ruling Workers' Party. He said North Korea could hold a national convention then - its first in nearly 30 years - to formally announce the successor.

Cheong noted that in the 1970s, Kim Il Sung, known as the "Great Leader," arranged for his son to take credit for a "70-day battle" before he was tapped in 1974 as his father's successor. The succession decision was made public at a 1980 convention, and Kim Jong Il - the "Dear Leader" - formally assumed leadership upon his father's death in 1994.