(CNN) -- North Korean leader Kim Jong Il's youngest son apparently was among more than 30 military promotions announced Monday by his father during celebrations of the Workers' Party of Korea's 65th anniversary, North Korea's state news agency reported.
Kim Jong Un has been widely rumored to be his ailing father's anointed successor.
Kim Jong Il's sister, Kim Kyong Hui, was apparently also promoted to general, according to the state-run KCNA news agency.
While it has been speculated that Kim Jong Un will succeed his father, details about him are scarce in North Korea and out.
"This appears to be the first public mention of Kim Jong Il's son by the North Korean media," said Mike Chinoy, the author of "Meltdown: The Inside Story of the North Korean Nuclear Crisis."
Kurt Campbell, the top State Department official on Asia, told CNN that "the United States is watching developments in North Korea carefully."
He said the United States will be talking to all its partners in the six-party talks about what transpired but it is "too early to tell" what was unfolding or how the United States should respond.
Two senior administration officials said this was expected and will likely pave the way for eventual transition of the son to replace his father.
Chinoy said the announcement was a step in laying down the foundation for a transition.
"It's significant that there was an explicit reference to him, and the position of general is a very senior one, obviously," he said.
CNN's Elise Labott contributed to this report.