Former Foreign Affairs Secretary Albert del Rosario arrived in Manila via Cathay Pacific Friday afternoon after he was denied entry to Hong Kong and deported back to Philippines by immigration authorities in the Chinese territory.

Del Rosario, a critic of Beijing’s claims to the disputed South China Sea, was behind two prominent initiatives against China, including a 2013 case at an international arbitral tribunal which eventually ruled against its claim over most of the resource-rich waterway.

Del Rosario said he flew to Hong Kong early Friday using a Philippine diplomatic passport but was taken to an immigration holding area on arrival, where he remained “for nearly three and a half hours”.

Del Rosario’s lawyer Anne Marie Corominas subsequently told AFP: “He’s been excluded and deported.”

She said he was already aboard a plane back to the Philippines and added that authorities had given no reason for denying him entry.

Hong Kong immigration officials had no immediate statement on the deportation but routinely decline to comment on individual cases.

Earlier del Rosario had told local Manila television network ABS-CBN that he was given “no rational explanation” for his detention.

In March, Del Rosario filed a complaint against Chinese leader Xi Jinping at the International Criminal Court, alleging “crimes against humanity” over the supposed environmental fallout of Beijing’s activities in the disputed waters.

Hong Kong immigration authorities briefly held another Filipino critic of China, former Supreme Court justice and special anti-graft prosecutor Conchita Carpio Morales on 21 May when she made a private visit to the territory with her family.

Morales, who was also a party in the complaint filed by Del Rosario at the ICC, was released hours later, but chose to return to Manila instead.

Del Rosario said he had been in Hong Kong to attend a board and shareholders’ meeting of a private company, and had asked the Philippine foreign department to inform the territory’s authorities about his trip.

The former foreign secretary, who served under previous Philippine president Benigno Aquino, accused airport immigration authorities of acting “in violation of the Vienna Convention” on diplomatic privileges.

Aquino’s elected successor President Rodrigo Duterte has since largely set aside the South China Sea ruling to court Chinese trade and investments.