Sigley last posted a blog on the company's website on June 20, reviewing restaurants aimed at Pyongyang's middle-to-upper class. He last sent a tweet on June 24.
Tongil Tours says it was "the first tour operator to offer concentrated language study at a North Korean university in 2016," with the next such tour due to begin on Friday with an overnight train ride from Beijing to the North Korean capital.
"It's likely that a small action could have been considered a 'mistake' and he has been arrested as a measure of punishment," Choi Soon-mi, a professor on North Korean Studies at Ajou University's Institute for Unification near Seoul, said in a phone interview. "He is an Australian national, and not a US citizen -- so unlike Warmbier, it's unlikely that Sigley will be used by the North Korean regime" as a diplomatic tool, she said.
South Korea's foreign ministry released a statement Thursday saying it's "monitoring the situation, but there is nothing for our government to comment at this point."
Australian Finance Minister Mathias Cormann, who is in Osaka attending this weekend's summit along with Prime Minister Scott Morrison, told reporters the lack of a consulate in North Korea meant Australia's South Korean embassy has reached out to officials in the insular Asian nation. Morrison is due to have dinner Thursday night with Trump in Osaka.
"There is obviously some complications in providing consular assistance into North Korea," Cormann said. "We work through the Swedish government in North Korea and all of these steps are underway."