Was Alek Sigley detained to keep him quiet ahead of the Donald Trump meeting?

When US President Donald Trump stepped over the line dividing North and South Korea at 3.46pm last Sunday after shaking hands with Kim Jong-un, the moment had been a while in the planning.

Mr Trump actually mentioned his plans to visit the sensitive demilitarised zone and the possibility of meeting Mr Kim to the Washington political newspaper The Hill six days earlier, but their story was held at the request of the White House on security grounds.

But the North Koreans would have been told well in advance. The timing of the detention of Australian student Alek Sigley on the Tuesday of that week supports the theory posed by Sydney-based Korea expert Leonid Petrov - and shared by others - that Mr Sigley's mysterious detention was related to the Trump DMZ visit.

Zealous North Korean officials, knowing that a major political moment was coming, likely wanted to ensure the social media silence of a prolific western commentator like Mr Sigley, even if his writings were inoffensive to the country's regime, said Dr Petrov, who taught Mr Sigley at the Australian National University and remains friends with him.

When Swedish diplomat Kent Harstedt arrived in Pyongyang to negotiate the release of Alek Sigley, he did so the day after Mr Trump and Mr Kim's meeting.

President Donald Trump meets North Korean leader Kim Jong-un at the border village of Panmunjom in the Demilitarised Zone, South Korea on Sunday.Credit: AP

"Whoever made the decision to put [Alek] outside of the ability to communicate, probably had in mind national security for North Koreans," said Dr Petrov, now a senior lecturer at the International College of Management, Sydney.

"Alek is known as being friendly, so I'm sure they did it in a mild way, a sensible way. That's my theory and it still stands: he was deliberately cut out of communications and it was prompted by things happening on the Korean peninsula."

Australian student Alek Sigley, with Swedish diplomat Kent Harstedt (inset).Credit: Nine Newspapers

Mr Harstedt alluded to bigger things at play. As the Swedish special envoy to North Korea, he is the point man for many countries, including Australia, that do not have their own diplomatic presence in the reclusive country.

As Prime Minister Scott Morrison and his officials spoke to Japanese, South Korean and American counterparts at the G20 summit in Osaka about Mr Sigley's disappearance, Australia was also mobilising Mr Harstedt through the Swedish government.

Mr Harstedt won't reveal exactly what he said to North Korean officials after he landed on Monday in their capital Pyongyang. But he told The Herald and The Age that the quick release by Thursday should not be "simplified" as a response to the intervention by his team.

"There might be a more complicated explanation, for many reasons, for the timing and the way it happened," he said.

North Korean officials initially refused to admit they even had Mr Sigley in detention, Mr Harstedt said. But by early Thursday morning, Australian officials had received word that Mr Harstedt's team had confirmed the 29-year-old was detained and that his situation was being discussed in Pyongyang.

By mid-morning of that day, the Australian embassy in Seoul got word from the Swedish Ambassador there was a strong possibility Mr Sigley would be handed over to Mr Harstedt's delegation at the airport as they left North Korea. The Australian government quickly dispatched two officials to the airport in Beijing, to which Mr Sigley would be flying.

Mr Sigley has been a frequent writer about North Korean food, culture and society as he led trips to the country with his company Tongil Tours. His business partner Michelle Joyce doubts Mr Sigley was detained over any serious issue. This was a view also expressed by well-informed sources.

Ms Joyce said Mr Sigley and the company had built strong relationships in North Korea, which meant it was unlikely he would have been targetted out of suspicion he'd done anything wrong.

"Maybe it was something that was part of the procedure," she said. "They make sure that foreign students that have access to communications don't say anything around the time of a major event. Sometimes people are instructed not to talk to others in those periods.

"I think that is a good theory," she added. "I don't know that's what happened, but it's a good theory."