Three Sydney men have been charged with more than 70 offences after an investigation into the alleged possession of illegal military-style guns by a group with suspected extremist ideology.

The trio, aged 26, 29, and 30, are due to face a Sydney bail court on Saturday after their arrest on Friday by counter-terror police.

Police seized 14 weapons over the course of the five-month investigation including an MK 15 assault rifle, a pump-action shotgun and a 9mm Glock pistol.

Two banana magazines and 523 rounds of ammunition were also found.

One man, a 29-year-old from Bankstown, is facing 45 charges including 18 counts of offering to supply a pistol to a person unauthorised to possess it.

The other men, from Condell Park and East Hills, also face gun supply charges.

None face terrorism charges.

Australian Federal Police Assistant Commissioner Scott Lee on Friday said the investigation began in January following reports of a person with “extremist sympathies”, who was allegedly “aligned to the Islamic State ideology”, supplying firearms.

“We’ve captured evidence in terms of the extremist beliefs that are consistent with Islamic State and that’s obviously part of the information that we obtained that caused us such concern,” Mr Lee said on Friday.

“There’s no evidence (the man involved wanted to join ISIS) … but certainly the evidence is that he’s supportive of ISIS and was looking to provide funds to Islamic State if possible.”

Mr Lee also said there was no evidence of any plan to mount a terrorist attack.

-AAP