An anonymous caller rang the National Security hotline on the weekend before the Lindt cafe siege to tip off authorities about the extremism of Man Haron Monis, urging authorities to look at his website, it's been reported.

The Australian Security Intelligence Organisation (ASIO) and the Abbott government was aware of the call within the 48 hours leading up to the siege, News Corp Australia reported on Sunday.

The caller did not suggest that Monis had a gun or that he was planning a terrorist act or that he had talked of any plans to take hostages but urged officials to "take a look at this man's website".

ASIO is understood to have looked at Monis's website as result of the phone call.

They found Monis had 14,000 likes on Facebook from supporters, had a number of websites, a Twitter account in support of Islam and jihadism but there was no mention of a planned terrorist attack, News Corp reports.