An Australian nun who angered the Philippine president by joining anti-government protests has criticised his “reign of terror” after being kicked out of the country.

Sister Patricia Fox, who arrived back in Australia on Sunday morning, said of Rodrigo Duterte’s violent crackdown on the drug trade: “The human rights abuses are just increasing and it’s a reign of terror. Of tyranny.”

Fox said she came to Duterte’s attention after going on a fact-finding mission in the president’s home province of Mindanao. The inquiry documented 54 cases of killings, torture and illegal detentions as well as harassment and intimidation.

“There’s been a culture of impunity for a long time but it’s getting worse,” she said. “Working with the peasants we had heard a lot of stories about extrajudicial killings, people in jail for trumped up charges, torture ... and so we went down to document it.”

There have been up to 20,000 extra-judicial killings as part of the anti-drug crackdown.

In Melbourne airport’s arrival hall, where she was greeted by a chanting crowd, friends and banners, Fox said: “I’m so happy to be back but I’m sad at the same time … It was really really hard leaving.”

Fox left the Philippines for Australia on Saturday night. The Bureau of Immigration ordered her to be deported in July, put her on a blacklist and then downgraded her missionary visa to a temporary visitor’s visa, which expired on Saturday.

On Sunday, Fox called on the Australian government to stand up to the Philippine president.

“I think they need to [be more forceful] ... we have to start being responsible for what’s happening over there,” she said.

The nun said she had been blacklisted from the country and would not be able to return until Duterte is no longer president.

Duterte has bristled at criticism of his leadership, particularly by foreigners such as Fox, who he says have no right to meddle in the Philippines’ domestic affairs. Most of the criticism has focused on his bloody anti-drug campaign, which has alarmed western governments and rights groups and prompted two complaints of mass murder before the International Criminal Court.

During a farewell news conference in a Catholic school before leaving for Manila airport on Saturday, Fox said: “Pope Francis said that if you’re a Christian and there’s massive human rights violations ... you should take action, make noise. Where the oppressed are, the church people should be there, not only always talking but with them and hopefully more vocal.”

Fox told the Associated Press separately by phone that Duterte’s anti-drug crackdown was “horribly barbaric” and she vowed to return to the country if allowed to resume her 27 years of missionary work for the poor.

“I know a lot of mothers, wives who have lost someone,” Fox said. “You have no right to take a life just like that without justice.”

The Philippines’ immigration bureau said Fox violated her missionary visa by venturing far beyond her community in suburban Quezon city in metropolitan Manila and interfered in domestic politics by joining protests and news conferences that tackled “political and human rights issues against the government”.

Aside from Fox, the government has separately blocked a critical Italian politician, Giacomo Filibeck, and another Australian, Gill Hale Boehringer, from entering the Philippines this year.

Members of the Phillipines Australia Solidarity Association were at Melbourne airport to welcome Fox home and praised her courage.

“We look forward to once again stand with her in the struggle for social justice and human rights in the Philippines and Australia,” a PASA spokeswoman, May Kotsakis, said.

• Australian Associated Press and Associated Press contributed to this report