"Our training overseas has never been secret. People know where we train, openly," Defense Minister Ng Eng Hen said Tuesday.

He added that Singapore had played a positive role in improving cross-strait relations between China and Taiwan.

Teaching Singapore a lesson?

Zhang Baohui, a professor of political science at Hong Kong's Lingnan University, said that Singapore had a long-standing defense ties with Taiwan and has often used the island for training drills given a lack of space in the crowded city state.

"I don't think that China has given Singapore a public rebuke for this before," Zhang said. "I think the real issue is that China thinks Singapore has turned into a quasi US ally."

"In the context of deteriorating relations, it could be a Chinese strategy to teach Singapore a lesson and a way to indicate their unhappiness," he added.

Singapore has strengthened military ties with the US and taken a tough stance on the South China Sea dispute, urging China to abide by an international tribunal that ruled its claims to the waters were unlawful, said Zhang.

Taiwan's Defense Ministry declined to comment, saying the troop carriers didn't belong to its military.

Singapore's Ng said that hoped the reasons for the vehicles' seizure would be made clear after a meeting Tuesday between Hong Kong officials and the commercial shipping carrier APL.

Hong Kong's Customs and Excise Department said the case is under investigation.

Role model?

"Singapore prides itself on its rule of law and its place in the international community and this complicates China's interests and what happens in its sphere of influence," she said.

Chiu added that Beijing was also likely sending a warning signal to Taiwan's new President Tsai Ing-wen, who is from a traditionally pro-independence party.

"It seems like Beijing is starting to feel it needs to be more heavy handed and nip these things in the bud," said Chiu.