MELBOURNE, Australia — Anti-war protesters clashed with police on Wednesday outside a military arms convention in the Australian city of Melbourne.

Protesters hurled bottles, rocks and horse manure, a police statement said. They also sprayed officers with liquid irritants, some of which were identified as acid, police said.

Police retaliated with pepper spray, flash distraction devices and rubber bullets, which are designed to inflict pain without penetrating the skin.

At least 24 officers required medical treatment. Police arrested 39 protesters for offenses such as assault, arson and blocking roadways.

“Victoria Police is appalled at the behavior of some of the protesters,” the statement said, referring to the Victoria state force.

Around 1,800 police officers have been deployed to a Melbourne convention center where the Land Forces International Land Defense Exposition is taking place through Friday.

Some of the convention attendees also were assaulted, police said.

Protesters also threw rocks, horse manure and tomatoes at police horses and officers with shields and wearing riot gear. A police officer on horseback struck a protester with a riding crop and a line of police were seen forcing protesters away from the convention center.

Police said some protesters targeted the horses, but no animal sustained serious injury.

Roads have been closed and traffic was disrupted by the protests, organized by Students for Palestine and Disrupt Wars groups. The organizers hoped up to 25,000 protesters would turn out.

Police estimated 1,200 protesters had surrounded the convention center by noon.