Police believe the alleged Anzac Day terrorism plot was partly payback for the death of teenager Abdul Numan Haider in September and was likely to consist of an attack in the south-eastern suburbs of Melbourne, Fairfax Media has learnt.

It is also understood that some of the young men arrested in counter-terrorism raids on Saturday morning are believed to have been with Haider before he launched his knife assault on two police officers that ended in his being shot dead in September.

In a further extraordinary development, police announced late on Monday that a 14-year-old boy in Britain had been arrested in connection with the alleged plot at the centre of Saturday's raids.

A spokeswoman for the Australian Federal Police confirmed "a link between the arrest of a 14-year-old boy in Blackburn, Lancashire in the United Kingdom on Saturday with Operation Rising".

"Investigators received information from UK authorities after they allegedly uncovered communications between the teenager and a man in Australia," the spokeswoman said.

Detective Chief Superintendent Tony Mole from the Greater Manchester Police said in a statement that the communications they had uncovered related to "what we believe is a credible terrorist threat".

As the dust settled on the weekend raids of Melbourne homes by Victorian and Federal police, Prime Minister Tony Abbott said he meant to use his visit to Turkey for Anzac Day to press Turkish authorities to clamp down on foreign fighters crossing through the country to Syria and Iraq.

"Obviously, Australians who have gone to fight with the death cult have mostly gone through Turkey. So, I will be talking to the Turkish leadership about what can be done to better police that border and to better ensure that people who have no reason to be going there are prevented from being there," he said.

"It is absolutely critical that as far as humanly possible, we stop gullible, impressionable young Australians from going to places where they could very easily be killed or they could get caught up in something which is in no one's interests."

Sevdet Ramdan Besim, 18, of Hallam, has been charged with conspiracy to prepare or plan terrorist acts, and has been remanded to appear in court on Friday.

Another 18-year-old who cannot be named was still being held on Monday under a preventative detention order while a third man, also 18, was expected to be charged on weapons offences. Two other men arrested were subsequently released without charge.

Fairfax Media has been told that the alleged plot involved a target in south-eastern Melbourne and that it was at least in part payback for Haider.

Haider was shot dead in September after allegedly attacking two officers with a knife outside Endeavour Hills police station.

A security source said that "it is believed that there are a number of those individuals [arrested on Saturday] that were with him before he went to the police station involved".

The alleged plot police say they foiled was reportedly to involve the beheading of a police officer at a suburban Anzac Day service.

Channel Seven reported on Monday night that the alleged plan was to run over an officer, behead them and take their weapons.

Haider was reported to have been with a number of other men at a fast-food restaurant shortly before he went to the police station to meet with the officers.

The source added there was a "definitive geographic location they were looking at" in the south-eastern suburbs of Melbourne.

As reported by Fairfax Media on Monday, police are looking intently at the role played by Islamic State fighter and recruiter Neil Prakash, who goes by the jihadist name Abu Khalid al-Cambodi and is believed to have helped inspire or encourage the alleged plot.

He is understood to have had direct communications with members of the group arrested on Saturday.

Greg Barton, a terrorism expert at Monash University, said one outstanding question was whether the young men were being groomed only by Prakash or also by some older and more senior extremists in Australia.

"I'm sure that's an issue the police are trying to get on top of," he said. "It could be somebody older, wiser, low key but who's been playing an instrumental role. That's the big question."

He said such recruiting aimed to "make them feel pretty important … persuading them they're really special and playing a special role".