Speculation of a high-level purge in North Korea’s leadership has grown after it was learned a close aide to the country’s leader, Kim Jong Un, appeared to be missing from a gathering in the capital of Pyongang. Kim has executed about 70 officials to solidify his position as the country’s unchallenged leader since his rise to power in 2012, according to a monitoring group in South Korea, the Wall Street Journal reported Thursday.

Choe Ryong Hae was seemingly left off of a list of about 170 names of organizers of a funeral for a senior military figure Sunday, and was then nowhere to be found among mourners at the funeral Wednesday, according to analysis of video footage from the event, the South Korean monitoring group said. Choe was an emissary to several countries, and the son of a noted armed forces minister. A South Korean government spokesperson said the omission of his name from the funeral list was unprecedented.

Choe may have been sent to an institution for ideological training, a South Korean intelligence official said. Although the reason for the suspected purge was unclear, North Koreans are required to show unquestioned support for Kim, and those whose loyalty has been questioned have often been punished or required to undergo additional training.

Choe was seen last week, however, so other South Korean officials were skeptical of the purported purge, Voice of America News reported

Several high-profile leaders, including a former uncle of Kim and a defense minister, have been purged in the past. Speculation has mounted that both men likely were executed.

North Korea is considered to have among the world’s most repressive governments. It is said to maintain secret labor camps for government opponents where torture and starvation are routine. Religion and free speech in the kingdom are virtually nonexistent, and denial of basic rights is widespread, human rights groups charge.

Noticed absences of senior officials from official state events have regularly prompted speculation of a possible purge. Purges generally have raised questions about the regime’s long-term stability and the possibility of growing internal dissent.