State security guards stormed a demonstration on Monday in Phnom Penh and beat the technical supervisor of Licadho, one of the country's most prominent rights groups, as hundreds of marchers protested against land seizures. The march to belatedly mark World Habitat Day began in heavy rain at the former site of the Dey Krahorm neighborhood, where residents were violently evicted by a private company in 2009. Evictees and land rights activists were hoping to march to the Land Management Ministry to deliver a petition denouncing such seizures. Dozens of police officers-outnumbering the initial gathering-moved the protesters northward as it gathered more participants. The crowd had grown to about 300 as it moved down Sisowath Quay, past the Royal Palace and away from the Land Management Ministry. Tensions came to a head at about 9:30 a.m. when Daun Penh district security guards blocked the path of protesters attempting to change course and rushed the crowd, destroying protesters' banners and photographs of jailed rights workers, and attacking Am Sam Ath of Licadho, who was attending as an observer. Mr. Sam Ath-as well as other witnesses-said he had been calling for calm when the guards turned on him and others. He was hit in the head and face and suffered cuts and bruising. Others were also left bloodied. "I told them, "Please don't use violence.' And they started beating me," Mr. Sam Ath said. "It shows that Cambodia doesn't respect human rights." The protesters-some wearing the black T-shirts from the "Black Monday" campaign-had been moving north on Sisowath Quay along the riverside before turning around near Wat Ounalom. At Street 178, police blocked the way, pushing the march west on to the tree-lined street and toward the Royal University of Fine Arts. The protesters got as far as Street 19, where they were confronted by dozens of guards in five security guard trucks. Staring down the crowd, district security guard chief Kim Vutha asked: "Who are your leaders? Why do you pass here?" Bov Sorphea, one of the organizers, responded that there had been a road block. In response, Mr. Vutha said to his guards: "Let's move forward." As the guards rushed into the crowd, one of them smashed a model house being used as a prop, and another chased a drummer into an art gallery. The guard emerged with a red drum, and was pursued by protesters who tried to grab it back. Many in the crowd scattered. City Hall later said the guards had been provoked and that protesters should not have attempted to evade the cordon. "We tried to round them up to rally at Freedom Park, and while traveling they caused chaos," said Met Measpheakdey, a municipal spokesman. "That was one of the reasons we didn't want them to go against what we allowed." "Some female protesters in the march also used umbrellas to beat our security guards," he added. "We haven't decided yet whether to take legal action against them." Chan Puthisak, an evictee from Phnom Penh's Boeng Kak neighborhood, said he was pushed against a parked car and one of the security guards ran toward him as he used his smartphone to record a video. "I raised my arms. They just beat me," he said. "Am Sam Ath came to stop the violence. So he was beaten instead of me." After someone struck him on his head with a fist, Mr. Sam Ath was swallowed into a mass of ponchos as photographers and television cameramen circled the group. Mr. Sam Ath said by telephone from the Licadho office in the afternoon that he had filed a complaint about the attack at the Chey Chumneah commune police station. "They beat me on the mouth, eyebrows, nose and jaw, and bruised the back of my neck," he said. In a statement issued later in the afternoon, and signed by 60 organizations, Naly Pilorge, director of Licadho, said the attack was the latest example in a long line of peaceful protests suppressed through violence. She described it as "a favored strategy for authorities terrified of citizens claiming their rights." "It remains to be seen whether this case will also-like so many of the others-result in complete impunity for the perpetrators," Ms. Pilorge said. "It is long overdue for the courts to start prosecuting para-police officers involved in systematic and recurring acts of violence." After the scuffle on Street 178, the marchers eventually arrived at Freedom Park at about 10:30 a.m., where an official from the Land Management Ministry received their petition, and a group of police officers came to return the confiscated drum. Hoeu Chanda, the ministry's deputy director-general for the general department of housing, promised to forward the petition. "Please, brothers and sisters, place your hopes on the government, especially the Land Management Ministry," Mr. Chanda said.