In his first announcement as Immigration Minister this week, Mr Dutton said customs officers would be able to carry guns and personal protection equipment at all Australian airports. The decision, which came into effect on Wednesday, was made to ensure officers could be respond to a number of potential "border-related threats" across an "evolving transnational crime and national security environment".

"The government is committed to ensuring that the future Australian Border Force is as well trained and well equipped as possible, to ensure that the public is protected from the range of new and emerging threats our nation faces at the border," a spokesman for Mr Dutton said.

But the overhaul of the Immigration Department to guard the country's borders, rather than focus on settlement and migration, is causing rifts.

Fairfax Media understands tensions within the department are rising before the two departments merge. More than five senior immigration staff recently left the department after former Customs chief executive Michael Pezzullo was announced as immigration secretary in October.

Former deputy secretary Mark Cormack has since left the department, while another former deputy secretary, Elizabeth Cosson, moved to the Health Department. Dr Wendy Southern, who was deputy secretary of immigration policy and chairwoman of the Irregular migration research advisory group, has also left.

The department confirmed a "small number" of senior executive staff had recently left the department.

"It is common for senior executives in the Australian Public Service to transfer from one agency to another. The senior executives concerned leave the department with the best wishes and full support of the secretary," said a departmental spokesman.

This week, Mr Dutton described the Australian Border Force as "a single frontline operational border agency with statutory responsibilities to enforce our customs and immigration laws".

"Its focus will be getting on with the job of border protection and building a system where criminals are faced with the hardest borders possible, but legitimate traders and travellers are unimpeded by border processes," a spokesman for Mr Dutton said.

And in a sign of the renewed focus of the department, during an Australian Strategic Policy Institute speech on December 4, Mr Pezzullo said as secretary he was charged with "protecting our borders".

"I prefer to see borders in a very different way. I see them as mediating between the imperatives of the global order, with its bias towards the flow of people, goods, capital, data and knowledge, and the inherent territoriality and capacity for exclusion which comes with state sovereignty."

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