There has been an increased level of “terrorist chatter” in the wake of last week’s Sydney cafe siege and a terrorist attack remains likely, Tony Abbott says.

“The terror threat remains high,” Abbott told reporters on Tuesday afternoon. People “with evil intentions” were willing and able to “do us harm”, he said.

A high alert level means an attack is considered “likely”.

Abbott reiterated that warning, but urged people to go about their lives as normal during the festive season.

“[Be reassured] that security agencies will be working around the clock to keep us as safe as possible,” he said.

Agencies were “doing every thing they can to monitor and disrupt” threats to national security.

Members of the national security committee of cabinet (NSC) met for the first time since the new ministry was sworn-in on Tuesday morning.

Abbott briefed new members of the committee, including the new defence minister, Kevin Andrews, and the new immigration minister, Peter Dutton, on the “heightened level of terrorist chatter” following the siege by gunman Man Haron Monis.

The prime minister refused to link the siege with Islam in the days following the attack, but on Tuesday labelled the siege, which ended in the death of Monis and two hostages, “the Martin Place brush with terrorism”.

An inquiry is under way to investigate how Monis got hold of his weapon, and how he fell off Asio watchlists.

“All of our agencies are asking themselves, how could this person have slipped through the net?” Abbott said.

Monis carried out the attack while on bail for being an accessory to the violent murder of his former wife, and numerous sexual assault allegations.