A man died and 130 people were injured on Friday as pro-reform protesters and government supporters clashed in Amman, in what the prime minister said was an Islamist attempt to "create chaos."
"Khairy Saad Jamil, 55, died today at the Prince Hamzeh Hospital" in Amman, a medical source told AFP without specifying the cause of death.
It was the first death since the outbreak of pro-reform protests in Jordan three months ago.
Another medical source at the hospital said the man had "received blows to his chest, and his teeth were broken."
But police chief Hussein Majali told a news conference that Jamil "died of a heart attack".
"There were no signs of beating on his body," he said.
Jamil's son insisted that his unemployed father "got several blows to his body, leading to his death."
"Our family is in the hospital now. We will not move until officials come to us and explain what really happened," he said.
There were conflicting reports on the number of people injured.
A medical source said 130 people, including a policeman, were injured in the clashes, including two in "critical condition."
However, police said in a statement "60 civilians and 58 members of police, including a sergeant and a captain were injured. All of them were hospitalised."
"The security forces had to put an end to the gathering after the two sides clashed," the statement said. "Attempts by Amman's governor to calm things down through dialogue have failed and provocations and stone-throwing from both sides continued, prompting police intervention."
An AFP journalist at the scene said police used water cannons to break up clashes between students protesting to demand reforms and government supporters.
"Police arrested eight people from the two sides for interrogation. An investigation is currently under way," Majali said, after anti-riot police broke up a protest camp for the students.
The clashes erupted after around 200 government supporters hurled large stones at more than 2,000 young demonstrators from different movements, including the powerful Islamist opposition, urging regime reforms and more efforts to fight corruption, an AFP journalist reported.
Blood stains could be seen at the site of the demonstration next to Amman's Interior Circle, or Gamal Abdel Nasser Square.
Prime Minister Maaruf Bakhit accused the Islamist opposition of seeking to sow "chaos" in Jordan, while the leader of the Islamic Action Front party said the government carried out "crimes against humanity."
"The government of Maaruf Bakhit has given proof that it does not believe in the reforms, it is a government with blood on its hands which today has committed crimes against humanity," IAF chief Hamzah Mansur said.
"Young people had assembled and were acting in a civilised manner. They did not deserve that sort of treatment."
Bakhit slammed the Islamists and said on state television: "The government has accurate information that the Muslim Brotherhood has mobilised the protesters."
"We have invited the Muslim Brotherhood for talks, away from protests and demonstrations, but apparently they have agenda to create chaos in the country," Bakhit said.
On Thursday night, 50 "loyalists" attacked the young protesters with stones after police cut power supply, injuring at least 30 people, protesters said, adding that police who surrounded the scene did not intervene.
The students want corrupt officials to be put on trial and security services to stop interfering in their affairs.
"The revolution is happening all around us," they shouted. "Jordan, your turn is coming."
"We want constitutional amendments to have parliamentary governments," said Alaa Fazaa of the Jayeen (We are Coming) group.
The protesters also included some expatriates.
"I am here today to express solidarity with the Jordanian people and back democracy and justice," Lise Olivarius, 25, of the ActionAid international charity, told AFP.
Since January, left-wing activists have joined forces with nationalists and the Islamist opposition in calling for far-reaching political reforms and an end to what they say is rampant corruption.
Elsewhere, thousands gathered in Al-Hussein Gardens west of Amman to express loyalty and allegiance to the king, dancing to national songs and waving large national flags and carrying pictures of the monarch.