Australian Prime Minister Tony Abbott said spies have detected increased levels of "chatter" among "terrorist sympathizers" following last week's deadly attack in Sydney's Martin Place and that an additional attack is "likely," reported the Herald Sun.

"Our police forces and our security and intelligence organizations are doing everything they possibly can to monitor and disrupt all the threats to our security," Abbott told reporters in Sydney.

Abbott said he was briefed by the head of the ASIO spy agency and the Australian Federal Police Commissioner during a national security meeting, and that people should go about their lives as normal despite the development, according to the Australian Broadcasting Corporation.

"The briefing from the security agencies today indicated there has been a heightened level of terrorist chatter in the aftermath of the Martin Place siege," he continued, the Herald reported. "That's why it's important that people remain alert and aware as well as reassured that our police and security agencies are doing everything they humanly can to keep us safe."

Security and police forces have been ramping up their presence and security measures ahead of a number of major events set to take place in Australia, including the World Cup cricket, Australian Open tennis, and the Boxing Day Test at the MCG, the Herald Sun reported.

"As you'll all understand, at this level, an attack is likely, we don't know when and how an attack may come, but we do know there are people with the intent and capability to carry out further attacks, and that's why it's important that as well as being reassured that people are aware of the reality of these times," Abbott said.

The terror alert level was raised to "high" in September in response to perceived threats from the Islamic State group.

Abbott said the alert level will remain the same and not be raised to "extreme."