Angus Taylor has suggested the Australian children remaining in a Syrian detention camp are “ISIS sympathisers” as the Liberal party ramps up its rhetoric against the families of dead or jailed Islamic State fighters.

The opposition leader also chided a member of the press for attempting to force his response on why the group of 23 children and 11 women should be another country’s responsibility.

“Either you’re an activist or a journalist, you need to make up your mind. You need to make up your mind which one you are,” Taylor said.

In a combative press conference ahead of question time on Monday afternoon, a reporter asked Taylor: “On branding them ISIS sympathisers, do you count the 20-odd children in that group as also being ISIS sympathisers?”

“They are ISIS sympathisers. Let’s be clear that this is a group who have gone to the Middle East to support ISIS … there is no ambiguity about that,” the opposition leader said.

“We must shut the door to ISIS sympathisers. We should have values-based and belief-based tests on who comes into this country and those who believe in this ideology, the ISIS ideology, are not welcome in this country.”

The comments came as the shadow home affairs minister, Jonathon Duniam, described the under-18 cohort as “so-called children”.

The group of 34 women and children – the wives and children of slain or jailed IS fighters – remain living in al-Roj detention camp in north-eastern Syria where the squalid conditions are described as “life threatening”.

Some of the children, who all hold Australian citizenship, were born in the camp and have never left.

The Guardian spoke with a number of young children at the camp last week, including six-year-old Layla, an Australian girl born in the camp who imagined Australia as place with “an ice-cream shop” and where Bluey and Bingo live.

Duniam said it was important to have compassion for the children but suggested, without providing evidence, that many were closer to adulthood in age.

“But that does not mean we need to sacrifice national security, and at this point in time, I don’t know how many of the cohort, so-called children, are below the age of 17,” Duniam said.

“If people in their minds think this is a bunch of two and three-year olds who are still learning to walk and talk, this is not the cohort we’re talking about. These children are a range of ages, and the government don’t have a handle on what sort of a risk they present.”

Under the Passports Act, citizens are entitled to a passport but there are some exemptions for people who have an active arrest warrant against them or where someone might “prejudice” the security of the country.

One woman within the group has been issued with a temporary exclusion order in February, banning her entry to Australia for up to two years.

The Albanese government has insisted it is not actively assisting the group’s repatriation to Australia but conceded there are few avenues available to prevent the group from returning.

The Coalition has said it will introduce a bill to make it an offence to provide assistance to repatriate people involved in terrorist organisations without prior approval.

The Greens senator, David Shoebridge, criticised Taylor for using the children as “political pawns”.

“When Angus Taylor comes here as the leader of a major political party in this country … and calls her a terrorist sympathiser, people can see through that,” he said.

“They know a little six year old girl, isn’t that, and it does him absolutely no credit to sink to those moral libraries and to try and weaponise kids in a detention camp.

“But when Angus Taylor tries to use these children as political pawns like this, he debases politics. He debases his party, and he debases himself.”