(CNN) -- A Jordanian official ordered an investigation Saturday to look into police officers' attacks on pro-reform demonstrators in Amman, state-run media reported.
Riot police punched, kicked and beat protesters with sticks Friday on the streets of Amman, according to CNN reporters on the scene. Several journalists were among those caught up in the violence, in some instances attacked by police.
Police Capt. Mahmoud El-Khatib initially said that authorities only used "appropriate force" to prevent even worse bloodshed among what he called two groups of protesters -- one backing the government, the other calling for reform.
But witnesses said there were no such rival groups, blaming police using batons and other means to beat back protesters.
Lt. Gen. Hussein Majali, the head of Jordan's public security department, on Saturday described the incident as a "police attack on a pro-reform march in Amman," according to the Petra news agency. This same report said the demonstration was organized by the Muslim Brotherhood and youth groups, which is distinct from its account the previous day.
Majali called for the creation of a panel of "senior officers" to investigate, a probe that began Friday night. This investigation, which will use "video material available to the committee," is expected to be done within 72 hours, followed by possible criminal trials.
Already, four policemen have been detained as suspects for their involvement in the violence, according to Petra, which was citing a statement from the Middle Eastern nation's public security department.
While there have been demonstrations in Jordan, as elsewhere in the Arab world, they have been largely peaceful and few have called for the ouster of its ruler, King Abdullah II.
Still, the violence Friday was at times stark.
One man lay on the ground, covered with blood-soaked tissues after a witness said he was hit in the head. Another man had a big gash on his arm. A woman, part of a group of 20 huddled together, said she felt shaky after being knocked in the head.
The state-run news report did not offer a casualty count, beyond claiming that 17 police officers were injured in the clashes.
There were "light to medium injuries to a number of journalists," Petra reported.
Mohammed Hanoun, a photographer, said he was attacked by police -- arguing with an official press liaison, who denied the media was being targeted.
"This is the moment I was hit," said Hanoun, showing a picture. "Do you see it? This is the last picture I took; he hit me with the shield."
Journalists typically wear orange vests in Jordan so they can be identified from protesters or police. Many media members took off their orange vests in solidarity with attacked journalists on Friday.
Salman Al Masaed, who was in the front row of the pro-reform demonstration, said he had no doubt that it was police -- and not rival protesters -- waging the offensive.
"We did not see a single person attack us," he said. "The only people that attacked us were the security forces, with their batons."