Australia is considering joining airstrikes against Islamic State fighters in Syria.

Prime Minister Tony Abbott told reporters on Thursday that while the United States has yet to make a formal request for airstrikes in Syria, "the matter has been raised."

Australian F/A-18 Super Hornet jet fighters have been striking Islamic State targets in northern Iraq from their base in Dubai since October last year.

Australia sent warplanes and military advisers into the Iraq campaign at the request of the U.S. and Iraqi governments. But Australia drew the line at airstrikes in Syria, where it does not recognize President Bashar Assad's administration.

While the opposition Labor Party supports Australian involvement in Iraq, it questioned the legal basis of Australian airstrikes in Syria.