Transport authorities are monitoring US-registered private aircraft visiting Australia after a threat by Muslim extremists to target and destroy American small jets.

The US Transport Security Administration warned late last week that a message posted earlier this month in Arabic on an internet forum explained how to identify American private jets and urged Muslims to destroy them.

"We call upon Muslims to follow and identify private civilian American aircraft in all airports of the world," the message said. "It is the duty of Muslims to destroy all types of private American aircraft that are of the types Gulfstream and Lear Jet and all small aircraft usually used by distinguished (people) and businessmen."

Owners and operators in the US are being urged to boost security measures and be alert for anyone masquerading as pilots, security officers, emergency medical personnel or uniformed personnel.

A spokeswoman for Transport Minister Warren Truss said the Government was monitoring the issue and receiving daily updates from an Australian-based TSA officer.