Canberra: The first group of refugees to be resettled under the Australian-United States resettlement deal flew out of Port Moresby on Tuesday morning.

The group of 25 men from the Manus Island detention centre will be joined within days by a second group of refugees currently housed on Nauru.

Beverly Thacker, public affairs officer for the US embassy in Papua New Guinea, said a total of 54 refugees from Manus and Nauru had been approved for resettlement “at this time”.

“Other refugee cases are under review,” Thacker told Guardian Australia. “They all have different time frames and we will expect that others will be advanced in the coming months.

The US agreed to take a number of refugees from Australia’s offshore detention facilities in a deal negotiated between the Australian prime minister, Malcolm Turnbull, and the former US president Barack Obama — and begrudgingly upheld by Donald Trump, who dubbed it “the worst deal ever.”

The original deal concerned the resettlement of up to 1,250 refugees from Manus and Nauru but the US is not obligated to take a certain number.

Thacker said the US would not comment on how many refugees might be approved.

She also would not say where they would be placed but said they would “go through the standard settlement process”.

The first group approved for resettlement were informed just under a week ago, after an extensive screening and interview process.

As of September 20, there were 928 men at the Manus Island centre and 1,135 people on Nauru, including 169 children.

The Human Rights Law Centre’s director of legal advocacy, Daniel Webb, said the first transfer flight was good news “for a handful of people” but left the bulk of the 2,000 people on Manus and Nauru behind.

“After four years of fear, violence and limbo, safety for a handful isn’t good enough,” Webb said. “It is our government’s responsibility to make sure not a single person is left behind.

“Anyone who can’t go to America must immediately be bought to safety in Australia.”

The Manus Island centre was scheduled to close on October 31 but the new PNG government is reportedly refusing to allow Australia to close the centre without a clear plan for the remaining detainees.

The planned closure was prompted by the PNG supreme court ruling that the men inside the centre had been illegally detained.

When contacted for comment, the Australian immigration department referred to a previous statement the immigration minister, Peter Dutton, made acknowledging the refugees’ expected departure.