Police fired smoke grenades at protesters gathered at riverside in Phnom Penh late this afternoon as a small group of demonstrators hurled rocks, shoes and pieces of metal back at them.

The violence erupted after protesters ripped apart police barricades and threw razor wire fences into the Tonle Sap and police responded by firing water cannons at them.

One young man was caught in the razor wire as police continued to spray water on him. He was rushed from the scene convulsing, and a first-aid worker who treated the young man said water had entered his lungs but that he had sustained no serious injuries.

A policeman was also reportedly injured during the standoff, which involved hundreds of military police, some armed with riot guns, shields, guns and truncheons.

Though police had said they were using tear gas it was clear to reporters directly on the scene that it was merely smoke.

Hostilities calmed down when several officials from the United Nations Office of the High Commissioner of Human Rights arrived at the scene and parked a vehicle directly in front of reassembled barricades.

The UN officials sat down with Phnom Penh municipal police chief Choun Sovann in a nearby bar to negotiate.

Afterward, Sovann told reporters they had seen with their own eyes that protesters had abused police who had deployed barricades at the site near the royal palace to protect King Norodom Sihanomi.

He questioned why protesters had moved to the site near Ounaloum pagoda when it had been made clear that the CNRP had permission to stage a non-violent protest at Freedom Park.

“At that time, I stayed close to his excellency Sam Rainsy, because he asked to pray in front of the royal palace, and we allowed him to do it following his will, and so I protected his security,” he said.

“Then he went back to Freedom Park, but his supporters did not go back, so I have to put one question to protesters, why do they want to stay here? What is their purpose?.”

Shortly before, Cambodia National Rescue Party president Sam Rainsy had arrived at the scene and instructed all protesters to stop the violence and either go home or return to Freedom Park.

“I would like to appeal to a group of youth or any people to stop the violence immediately. We don’t need to use any violence, so I would like to condemn anybody who uses violence or uses brick or blames,” he told the assembled crowd, before compelling protesters to go and enjoy music at Freedom Park.

The small group of protesters had come from Freedom Park, where the opposition is staging a three-day demonstration protesting the results of the July national election, which they claim was systematically rigged.