BEIJING, Jan. 8 (Yonhap) — China said Thursday that it has sent a message of congratulations to North Korea on the birthday of its young leader Kim Jong-un, expressing its hope Kim can oversee a “new achievement” in socialism.

Kim, who inherited power after the death of his father in late 2011, was born on Jan. 8 and is believed to be in his early 30s, but his age has not been officially confirmed.

“China and North Korea have a long-standing tradition of friendly exchanges. We have sent our message of congratulations,” China’s foreign ministry spokesman Hong Lei told reporters, when asked whether China sends such messages to North Korea.

“We hope that, under the leadership of comrade Kim Jong-un, North Korea can make a new achievement in its course of socialism,” Hong said.

Political ties between China and its only treaty ally, North Korea, remain strained, particularly after the North’s third nuclear test in February 2013.

However, few analysts believe that China will exert enough pressure on the North to give up its nuclear weapons because it could lead to the collapse of the North’s regime and hurt China’s national interests.

North Korea has not set a public holiday to mark the birthday of Kim and no celebratory mood was detected in reports by the North’s state-run propaganda machines on Thursday.

Some analysts in Seoul said North Korea may publicly mark the birthday of Kim about four to five years later, because it would be burdensome for the North’s regime to build a personality cult around Kim, given his young age.