Jordanian police beat protesters during a demonstration in Amman on July 15, 2011[AFP]

The Jordan Press Association says it plans to sue the police department after 15 journalists, including Al Jazeera's senior journalist in the country, were beaten up as they covered a demonstration on Friday in Amman.

The announcement comes one day after four policemen suspected of attacking the journalists were arrested.

"The union will file individual and collective lawsuits against the public security department," Tareq Momani, the JPA president, said on Sunday at a sit-in outside the association.

At least 17 people, including journalists and policemen, were injured on Friday when police tried to stop clashes between pro-reform demonstrators and government supporters in central Amman.

Yasser Abu Hilala, Al Jazeera's Amman bureau chief, said he was among those targeted by police.

"I was attacked as I was doing my job with other journalists," Abu Hilala said. "Several policemen and thugs tried to pull the cord of the camera and as I tried to stop them they started to punch and kick me."

"Al Jazeera has been singled out from the rest of the media outlets because they see [Al Jazeera] as instigators who highlighted what happened on [Friday 15 in Nakheel Square] ... This kind of brutality against media is unheard of in Jordanian history."

Abu Hilala said four of the injured journalists were still in the hospital and that unofficial pro-government websites had been calling for people to attack and kill him.

'Especially shocking'

Police used batons to break up Friday's clashes outside city hall, assaulting journalists wearing orange vests marked "Press".

"I apologise to journalists for agreeing with the police department to make them wear the vests. This was apparently nothing more than a trap," Momani said.

"The attack on the journalists reflects an alarming hostility by the security forces towards the media," Lamis Andoni, a political commentator, told Al Jazeera. "It is especially shocking because the head of the public security had given gurantees that journalists would be protected by the police."

"So far, people have been demanding reforms but such actions by security forces will only provoke more popular anger and more radical demands," she said.

A statement from the criminal investigation department said "[Chief] General Hussein Majali has formed a committee of inquiry into the attacks on the journalists who were simply doing their jobs".

The results of the probe were to be announced within 72 hours, it said, vowing to "refer to courts those who have a case to answer".

"These police measures are not enough. There are dozens of policemen who should be held accountable," Momani said.

MPs and Islamist leaders took part in Sunday's sit-in, and, during a parliamentary session, issued a statement condemning attacks on freedom of speech and expression, Al Jazeera's Nisreen El Shamayleh, reporting from Amman, said.

The statement stressed that parliament would not tolerate attacks on journalists, and said everyone linked to the violence must be held accountable.

"I salute the journalists. What happened will not silence calls for reform," Hamzah Mansur, head of the opposition Islamic Action Front (IAF), said.

"I congratulate our journalists who insist on reporting the truth about our people's grand aspirations."

Anger at the PM

Protesters are demanding that Maaruf Bakhit, the Jordanian prime minister, face trial over the incident.

About 400 people demonstrated outside his office on Saturday, condemning Friday's violence and demanding the resignation of his government and his trial.

"Freedom, freedom! No to martial laws. We say to the intelligence services that Jordanians are still alive," they chanted amid a heavy security presence.

The protesters carried banners reading: "The people want the downfall of the government. We want to put Bakhit and the attackers of demonstrators on trial."

Since January, Jordan has faced a protest movement demanding political and economic reforms and an end to corruption.