The 84-year-old former dean of Macquarie University’s law school has been detained in the Philippines over alleged political activities.

Prof Gill Boehringer, a human rights activist whose wife is Filipino, was detained at Manila’s international airport and denied entry into the country after arriving on a flight from China on Wednesday local time.

The Philippine Bureau of Immigration recommended that Boehringer, who is originally from the US, be blacklisted based on reports he took part in a rally in November 2015 in violation of an order “prohibiting foreigners from engaging in political activities in the Philippines”.

Boehringer told Reuters the accusation he had joined protests was “trumped up”.

“This is part of the government’s campaign to keep foreigners away from what they’re doing … the injustices, the killings, the disappearances,” he said.

The human rights group Action for Peace and Development in the Philippines, of which Boehringer is a member, said it condemned his detention and threatened deportation.

Its chairman, Peter Brock, who has known the law professor for eight years, said he was a “champion” for human rights, justice and accountability and “certainly not radical”.

He said Boehringer was aware there was a risk in going back to the Philippines after the Australian nun Sister Patricia Fox was ordered to be deported this year for her involvement in human rights’ protests.

“It’s not interference in another country to raise concerns about human rights violations,” Brock told Australian Associated Press. “You shouldn’t stay silent when things are happening in other countries.”

Boehringer’s lawyer, Maria Sol Taule, said she was negotiating with the bureau to allow him to stay in Manila because he was “medically unfit” to travel.

“He should be afforded due process to answer the allegations against him,” Sol Taule said. “Prof Boehringer is active in his human rights advocacies and solidarity with the Filipino people.”

Dr Geneve Rivera-Reyes from the advocacy group Health Action for Human Rights examined Boehringer while he was in detention and said it was “not safe” for him to travel again without medical clearance.

Rivera-Reyes said he was suffering from deep vein thrombosis and cellulitis on both legs.

“The Bureau of Immigration is being heartless in pursuing the deportation of Prof Gill Boehringer,” Rivera-Reyes said on Facebook on Thursday.

Australia’s foreign affairs department said on Thursday it was providing consular assistance.

