Malcolm Turnbull says people should defy terrorists by going about their lives following Saturday night attacks in the US.
The prime minister, who is in New York for the 71st session of the United Nations General Assembly, was responding on Sunday to an overnight blast in Chelsea and a mass stabbing in Minnesota.
Nearly 30 people were injured in the dumpster explosion in the fashionable Manhattan neighbourhood.
"We don't know what the motivations were," Mr Turnbull told reporters in Central Park.
"But it was clearly a deliberate explosion."
News that makes sense
Your trusted source for staying up-to-date with the world around you. Get free daily news updates and analysis, straight to your inbox.
At least eight people were wounded in the stabbing attack at a central Minnesota mall also on Saturday night.
Mr Turnbull said it was important to learn from the attacks but also to not be intimidated.
"You see today New Yorkers are going about their lives," he said, noting how packed the subway was.
"The one thing we can't do is let people who seek to do us harm, whatever their motivations may be, to coward us. We defy them by going about our lives in the normal way."
He said the Minnesota attack, reportedly claimed by Islamic State, was an example of a lone act attack, as seen in Australia.
"The key to prevention there is good intelligence," he said.
Mr Turnbull has already said he intends to talk up international collaboration in the battle against terrorism during meetings in the US.
He visited the 9/11 memorial and museum shortly after arriving in the country and will meet with Defence Secretary Ash Carter and senior national security and intelligence officials in Washington DC later in the week.
