A Sydney mother of four was told via text message that her sons had gone to Syria to allegedly fight alongside Islamic State militants.

According to Nine News, the mother believed her four sons aged 17, 23, 25 and 28 were holidaying in Thailand when she received a shocking message from them revealing their real location.

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“We made it Bilad al-Sham [an Arabic word referring to Greater Syria], we will see you in Paradise,” the text message read.

Thinking it was a joke, the mother went to the airport the following day to pick them up as planned and found no sign of them.

The brothers, who have not been named, are believed to have travelled to Turkey and then crossed the Syrian border to join in fighting with ISIL militants.

“My sons, you are dear to us,” the mother said in a statement. “You are good at heart. You have done nothing wrong. Come back. We love you.”

The men were not known to police nor were they on any terrorist watch lists.

The brothers are the latest in a spate of Australians travelling overseas to join the Islamic State.

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.