Four western Sydney brothers are suspected of travelling to Syria to fight with Islamic State militants.

The siblings are believed to have travelled to Turkey and crossed over to the Syrian border sometime in the past week.

• Islamic State leader’s death rumoured 
• The new face of Australian terror

Authorities were alerted by concerned family members after the brothers – aged 17, 23, 25 and 28 – left the country last Saturday and failed to contact home.

A spokesman for Immigration Minister Scott Morrison confirmed the minister had received the alert but could not retrieve the brothers on time.

He is due to address the media on Saturday.

The Australian Federal Police has admitted a number of Australians “not on anyone’s radar” have managed to slip out of the country in the past few days to join the jihadist group.