The head of Human Rights Watch who was barred from entering Hong Kong said on Monday he was saddened at how the city had deteriorated under pressure from Beijing, as he vowed to unveil his report in New York instead.

Kenneth Roth, the group’s executive director and an American citizen, returned to the United States after Hong Kong immigration authorities turned him away at the city's international airport on Sunday without explanation, according to the organisation.

He had planned to visit the city to launch the New York-based group’s “World Report 2020”, which includes a lead essay on the Chinese government’s “assault” on the international human rights system.

An Immigration Department spokeswoman said it would not comment on individual cases.

She added that when handling cases, the department would, in accordance with the laws and immigration policies, fully consider all relevant factors and circumstances of the case before deciding whether the entry should be allowed or not.

Roth said: “I had hoped to spotlight Beijing’s deepening assault on international efforts to uphold human rights. The refusal to let me enter Hong Kong vividly illustrates the problem.”

Roth, who had flown in from New York, later wrote on Twitter: “Despite my probing, the Hong Kong immigration authorities would say only (and repeatedly) that they were barring me for ‘immigration reasons’. They wouldn’t even own up to the real reason.”

“It's sad and troubling how quickly things have deteriorated under pressure from Beijing,” he added.

“Trying to silence the human rights messenger shows a determination to flout, not uphold, human rights standards.”

The group was expected to release its 652-page report at a news conference in Hong Kong on Wednesday. The report reviews human rights practices in nearly 100 countries.

Roth’s essay says the Chinese government is undermining the global system for enforcing human rights.

On his return to the US on Monday, Roth revealed he would launch the report at a news conference at the United Nations in New York on Tuesday “given that the authorities blocked me from entering Hong Kong.”

On December 2, Beijing’s foreign ministry spokeswoman Hua Chunying said the Chinese government would impose sanctions against Human Rights Watch and four other US-based non-profit groups that “played an egregious role” in the disturbances in Hong Kong, in its response to Washington’s endorsement of the Hong Kong Human Rights and Democracy Act, which could pave the way for diplomatic action and economic sanctions against the city’s government.

The other groups were the National Endowment for Democracy, the National Democratic Institute for International Affairs, the International Republican Institute and Freedom House.

The next day Hong Kong leader Carrie Lam Cheng Yuet-ngor said her government would follow up on the sanctions announcement.

Roth has visited Hong Kong several times, including to release a report on gender discrimination in the Chinese job market in April 2018.

The group also listed a number of other visitors who had been denied entry by Hong Kong immigration authorities, including a US photographer [Matthew Connors] who documented Hong Kong protests in January, US academic Dan Garrett last September, and United Kingdom-based founder of Hong Kong Watch Benedict Rogers in October 2017.

“This disappointing action is yet another sign that Beijing is tightening its oppressive grip on Hong Kong and further restricting the limited freedom Hong Kong people enjoy under ‘one country, two systems,’” Roth said, referring to the principle under which Hong Kong is governed.

Earlier this month, Human Rights Watch co-wrote an open letter to Lam, urging her to set up an independent commission of inquiry to investigate alleged excessive use of force by police in the more than seven months of anti-government protests in Hong Kong.

“An independent commission of inquiry is the first step to addressing the serious human rights violations against protesters since June,” said Sophie Richardson, China director at Human Rights Watch.