MANILA -- Hong Kong immigration authorities on Tuesday denied the entry of a former Philippine government official who earlier this year filed a complaint against Chinese President Xi Jinping with the International Criminal Court.

Conchita Carpio-Morales, former Supreme Court associate justice and ombudsman, and former Philippine Foreign Affairs Secretary Albert del Rosario, in March filed a case against Xi with the ICC in The Hague, arguing that the "massive" environmental destruction caused by Beijing's island-building in the South China Sea was tantamount to crimes against humanity.

In their letter to the ICC, Carpio-Morales and del Rosario urged the court to initiate a "preliminary examination" to "appraise itself of Chinese crimes committed not only against the Filipino people but also against people of other nations."

The ICC has not announced any action in the case.

Carpio-Morales's lawyer, Anne Marie Corominas, told the Nikkei Asian Review that it was "highly probable" that Carpio-Morales' role in the complaint against Xi was the reason why Hong Kong immigration authorities classified her as a "security threat."

"How can a 78-year-old former anti-corruption official be a security threat to Hong Kong and China?" Corominas said. "She is just there for a vacation with her family."

Carpio-Morales was scheduled to return to Manila on Tuesday evening after immigration officials rejected her entry at Hong Kong International Airport around noon, Corominas said.

Hong Kong legislator Ted Hui Chi-fung said the decision to bar Carpio-Morales from entering the city was unreasonable and not in line with the rule of law.

The move "looks like political reasons rather than security reasons were considered. Under the 'one country two systems' policy, the Hong Kong government has no legal basis to consider the court case that has nothing to do with Hong Kong," Hui said in a statement.

"Deportation based on a court case is plain barbaric," he said.

Hong Kong immigration officials could not immediately be reached for comment.

Both Carpio-Morales and del Rosario served under the administration of former President Benigno Aquino, who led an arbitration case against China over the South China Sea territorial dispute.

Current Philippine President Rodrigo Duterte reversed the hard-line China policy and embraced Beijing as a diplomatic ally after he assumed office in 2016.

The Philippines' Department of Foreign Affairs in Manila did not immediately respond to a request for comment.