A foiled terror plot in Sydney overnight is now being linked with Islamic extremism.

Police have arrested four men over an alleged plan to detonate an explosive device on board a long haul flight leaving Sydney.

The raids across Sydney were carried out by heavily armed police officers, and members of Australia's domestic spy agency.

READ MORE: Details emerge of foiled plot to down Australian plane

But a woman who says her son and husband were among those arrested in Sydney, has spoken with the BBC and denied they had any links to extremism.

Senior Police commanders say the raids were part of an alleged Islamic inspired plot.

Australian Federal Police Commissioner Andrew Colvin said officers became aware people in Sydney were planning to commit a terrorist attack using an "improvised device". 

As of yet, the four men in custody had not been charged by police.