SINGAPORE — Dickson Yeo, the Singaporean who was jailed in the United States for spying for China earlier this year, has been arrested under the Internal Security Act after serving out his US sentence.

He returned to Singapore on Wednesday (Dec 30), the Internal Security Department (ISD) said in a statement on the same day.

The department said: "ISD will interview Yeo to establish if he had engaged in activities prejudicial to Singapore’s security. Singapore will not allow our nationals to be subverted or used by any foreign actors for activities prejudicial to our security and national interests.

"The Government takes a very serious view of any Singaporean who enters into a clandestine relationship with a foreign government and engages in espionage or subversive activities at the behest of the foreign power. We will deal firmly with such individuals in accordance with our laws."

Yeo was convicted in the US to a spying charge and had been sentenced to 14 months’ imprisonment in October, having already spent 11 months behind bars. He was expected to be back in Singapore by January.

He had provided classified information to China by using his US-based political consultancy as a front for Chinese intelligence services between 2015 and 2019, according to court documents.

To do so, Yeo hired US military and government insiders with high security clearances to write reports for his consultancy, telling them they were meant for his clients in Asia.

Instead, Yeo sent the reports which he thought contained interesting information to his China handlers.

He was fully aware he was working for Chinese intelligence, having met agents in China dozens of times and was given special treatment when he travelled to China, court documents said.

The ISD noted that Yeo had admitted to the US investigators that "his previous intelligence taskings targeted other states apart from the US".

Yeo was a PhD student at the National University of Singapore's (NUS) Lee Kuan Yew School of Public Policy (LKYSPP). His candidature was terminated after the US court charged him for working as a foreign agent.

Court documents said Yeo was recruited by Chinese intelligence during his time in NUS.

Mr Bilahari Kausikan, a retired diplomat, had said Yeo's PhD supervisor was former LKYSPP professor Huang Jing, who was expelled by Singapore in 2017 for acting as a foreign agent of influence.

Mr Huang had since denied recruiting Yeo.

The Ministry of Home Affairs had said in July that an earlier investigation showed Yeo had not posed any direct threat to Singapore's security.