Attorney-General George Brandis believes that if police had not acted on Thursday it was likely extremists could have carried out an execution in Australia.

Australia could have witnessed a local beheading by Islamic State extremists if police had not carried anti-terrorism raids in two cities, Attorney-General George Brandis says.

More than 800 counter-terrorism police executed warrants across Sydney and Brisbane on Thursday, detaining 15 people and charging one person over an alleged terrorism conspiracy.

Senator Brandis said an operation had been underway since May and he understood the raids had taken on a sense of urgency.

“If ASIO and the AFP and the Queensland and NSW police had not acted today there is a likelihood this would have happened,” he told the ABC.

Senator Brandis, who earlier met with the Islamic Council of Victoria, said the government rejected the notion that Islam was intrinsically a violent religion.

“The suggestion that mainstream Islam is anything other than a religion of peace is arrant nonsense,” he said.

“Islam is one of the world’s great religions.”

The 500,000-strong Muslim community was one of the most law abiding and best educated communities in Australia, he said.

“It grieves me that people from that community would feel that their good name is being tarred by a relatively small number of dangerous people,” he said.

“It can’t be stressed often enough that we’re talking about a relatively tiny number of people – maybe 150 or so.”