Hundreds of people rallied at Darling Harbour in Sydney on Tuesday to protest against the Indo Pacific International Maritime Exposition, a three-day event billed as the nation's premier commercial maritime and naval defence forum.
Exhibitors include Israeli weapons manufacturers and other firms supplying the nation's military.
An attempted blockade of the biennial event escalated tensions with police as the conflict ebbed and flowed in the five-hour protest.
Palestine Action Group organiser Josh Lees was denied the opportunity to ask police a question at a press conference after the event.
NSW Police Superintendent Paul Dunstan told Mr Lees he would not talk to him until after the briefing.
"It's not the time nor place," he told the Palestine Action Group leader.
Thirteen people were arrested and two police officers injured in the clashes.
Police say there could be more arrests as they review CCTV footage.
Officers struggled to hold back the crowd as it surged about 8am before further clashes and more arrests about 11am as delegates inside waited to hear from Chief of Navy Vice Admiral Mark Hammond.
Four people were seen on the ground during the later flare-up while an officer had blood on his face from a cut nose.
A second officer was hit in the eye with paint, which needed to be flushed out.
Mr Lees said demonstrators were set upon as soon as they arrived towards their advertised assembly point near IMAX.
"We were attacked by police in a way which we haven't been for two years," he told reporters.
"(They) immediately started pepper spraying people, attacking people, riding horses into people."
More than 50 protesters were hit badly with pepper spray and another suffered a suspected broken leg, Mr Lees said.
Supt Dunstan said the group did not talk to police before the protest.
"There was certainly no approvals for them to come through," he said, adding he hoped to work with the group to avoid future clashes.
"What happened today was entirely out of character.
"All the goodwill and work with those groups has really been damaged from what has occurred today."
Much of the protest focused on the NSW government's role hosting and sponsoring the expo amid the conflict in Gaza.
"Chris Minns, blood on your hands," attendees chanted, referring to the NSW premier.
Addressing a report export controls were tightened on Tuesday, Defence Industry Minister Pat Conroy said the only export licences being approved related to maintenance, upgrades or manufacture of Australian Defence Force equipment.
"We haven't supplied ammunition or weapons to Israel over the last five years," he told reporters.
"The only export licences that are being approved right now (are) for ADF equipment that is going to Israel for either repair or upgrade or manufacture to come to back to Australia."
Government figures have consistently denied Australia exports weapons to Israel, although local companies have produced parts for F-35 jets used in the two-year bombing campaign in Gaza.
Mr Minns told ABC radio he was unaware of the circumstances surrounding the protests and had no input into decisions regarding Australia's relationships with foreign countries or arms manufacturers.
"They're not selling nuclear weapons down at Darling Harbour this weekend," he said.
Protesters have vowed to rally each day of the expo.
"We'll obviously continue to try to have a massive peaceful protest movement," Mr Lees said.
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