Former Taiwan leader Ma Ying- jeou's application to visit Hong Kong this week - in what would have been his first trip after stepping down as president - has been rejected by the Tsai Ing-wen administration on grounds of national security.

Mr Ma's office hit back, saying that to question his loyalty and raise the possibility he could leak Taiwan's secrets was not just disrespectful to him, but also damaging to the island's reputation as a democracy.

The exchange marks the first public row between the current and former leaders, following Ms Tsai's inauguration on May 20.

Mr Ma had been invited to attend the Society of Publishers in Asia awards ceremony on Wednesday. He wanted to deliver a speech on issues, including cross-strait ties, currently undergoing a tense phase.

Under Taiwan's rules, former officials with access to classified information face travel restrictions for three years after leaving office.

A task force was set up to review Mr Ma's application, and yesterday afternoon, Presidential Office spokesman Alex Huang told local media that it was rejected.

Mr Huang explained that Mr Ma had barely stepped down for a month, and possessed confidential information that requires a high degree of safeguarding.

At the same time, Hong Kong, being a part of China, is deemed a "highly sensitive" destination with regard to Taiwan's national security. There is also no system of cooperation between the security bureaus in Hong Kong and Taiwan.

The decision sparked an angry statement from Mr Ma's office, accusing Ms Tsai's administration of unprofessional ulterior motives, reported the Central News Agency.

The statement said that former president Lee Teng-hui and vice-presidents Annette Lu and Vincent Siew had made multiple trips abroad, without the opposition of national security authorities.

"It is not clear why there are suddenly such considerations this time round, and it raises questions of whether there were unprofessional calculations, motives and reasons."

It also said it had been transparent about the trip, providing the itinerary, details of the organisers, and Mr Ma's speech. He had planned a seven-hour stop in Hong Kong and would leave the very day he arrived.

"Yet, the possibility of leaking secrets is raised, and this is not just disrespectful to a former head of state, but hurts Taiwan's reputation as a democracy.

"It is hard to be convinced by the government's decision."