SEOUL, South Korea — South Korea believes North Korean leader Kim Jong Un may have sacked his uncle and de facto deputy, Jang Song Thaek, two South Korean lawmakers said.

Jang, a vice chairman of the National Defense Commission, hasn’t been seen since the public execution of two of his allies last month, opposition lawmaker Jung Cheong Rae said by phone Tuesday, citing South Korea’s National Intelligence Service.

Ruling party lawmaker Cho Won Jin said at a televised news briefing that the purge took place following a corruption investigation. Both Jung and Cho serve on South Korea’s parliament intelligence committee.

The NIS declined to comment on Jang when a call was made to its main phone number.

The removal of Jang may indicate that Kim is still trying to solidify his grip on power by purging top officials who gained prominence under his father Kim Jong Il, who died of a heart attack in 2011. In October, Kim replaced his chief of general staff for a third time since taking over the North’s 1.2 million-strong army.

“This could be a sign there’s a problem with Kim Jong Un’s grip on power,” Ahn Chan Il, who heads the World Institute for North Korea Studies in Seoul, said by phone. “I suspect there is a stability issue in the regime.”

SOLIDIFYING TRANSITION

Jang, who married Kim Jong Un’s aunt Kim Kyong Hui in 1972, was named to the post in June 2010 by Kim Jong Il.

At the time, the move was seen as solidifying the transition of power to Kim Jong Un, whom Jang backed as successor, Paik Hak Soon, a senior research fellow at the Seongnam-based Sejong Institute said in 2010.

North Korea is “conducting follow-up measures” against organizations affiliated with Jang after the purge, lawmaker Cho said. The government is mounting a campaign for “absolute loyalty” to Kim, he said.

During Kim Jong Il’s rule, the National Defense Commission was regarded as North Korea’s most powerful institution, and remains more important than both the nation’s defense agency and the ruling Korean Workers’ Party. Jang walked directly behind Kim Jong Un at his father’s funeral. Kim Jong Un chairs the National Defense Commission.

KIM'S WARNING

“Kim is warning the public with the executions, and it can only mean he’s feeling insecure about his power,” Lee Ji Sue, a professor of North Korean studies at Myongji University in Seoul, said by phone. “Kim just didn’t have enough time to build his own power base before his father died, and the economic situation right now just doesn’t help.”

Jang, one of the country’s leading economic policy makers who visited China in August last year, was reported by South Korean newspapers to have been demoted in 2004 for cultivating too much influence.

He was brought back to power in 2006 to head the Workers’ Party’s administrative department, overseeing the intelligence agency and other military institutions.

The disappearance of a senior official instrumental to Kim Jong Un’s succession isn’t unprecedented. In 2012, North Korea’s official Korean Central News Agency said that Ri Yong Ho, the general staff chief, had been removed from all posts, while all traces of his presence were eliminated from official footage and photos. KCNA gave no clear reason for the decision.

KCNA last reported on Jang in early November.

CORRUPTION INVESTIGATION

The corruption investigation into Jang’s allies may have been led by Choe Ryong Hae, North Korea’s top political military officer, as a result of a power struggle, and may actually show Kim’s strength, Cheong Seong Chang, a researcher at the Sejong Institute, wrote in an email.

“The executions and Jang’s removal from posts show Kim Jong Un’s power is very solid at the moment,” Cheong wrote. “I expect the race for loyalty will heat up in the ruling circle in the future.”

North Korea’s relations with the outside world have dipped under Kim, as the country tested its third atomic device in February and threated nuclear strikes against South Korea and the U.S. On Nov. 6, North Korea rejected the idea of a summit after South Korean President Park Geun Hye said she was willing to meet Kim if it led to concrete results.

The two Koreas remain technically in conflict after the 1950-53 Korean War ended without a formal peace treaty.

“Instability with Kim’s grip on power will continue, and he may try to ride it out by creating a military crisis with the outside world,” Myongji University’s Lee said. “With no aid and no dialogue, the crisis for the ruling class continues to deepen.”