Sydney, Dec 23 (IANS): Australian Prime Minister Tony Abbott Tuesday said there is a "heightened level of terror chatter" in the wake of the Sydney hostage crisis.

Seventeen people were taken hostage by Iranian refugee Man Haron Monis at Sydney's Lindte Chocolate Cafe Dec 15 that left three people, including him, dead.

The prime minister Tuesday convened the first meeting of the National Security Committee of the cabinet with new Defence Minister Kevin Andrews and new Immigration Minister Peter Dutton, the Sydney Morning Herald reported.

The National Security Committee was briefed on the development by intelligence officials, the prime minister said.

Abbott also urged Australians to celebrate Christmas as normal but be alert for any suspicious activity.

"The national security agencies indicated that there has been a heightened level of terrorist chatter in the aftermath of the Martin Place siege," Abbott said.

"That's why it's important that people remain alert."

The Australian Security Intelligence Organisation (ASIO) and the Australian Federal Police raised the national terror threat level from "medium" to "high" in September, meaning a terrorism attack was "likely".

The level remains unchanged despite the fatal siege and increased chatter, Abbott said.

Cafe manager Tori Johnson and barrister Katrina Dawson were killed when Man Haron Monis took 17 people hostage in the Lindt Chocolate Cafe Dec 15.