The conference, entitled "For reforms and against corruption," was being held at Salhub, 50 kilometres (32 miles) from Amman, and attended mainly by members of the Bani Sakher and Bani Hassan tribes, they said.
"The attackers suddenly began throwing stones at the participants and then fired in the air to disperse the gathering," one witness said.
"The tribal members then drew their weapons and also fired in the air, causing the attackers to flee," another participant said.
At least 35 people were slightly injured and 27 cars damaged, organisers of the meeting said.
Among those attending the conference were National Reform Front (NFR) head, former premier Ahmad Obeidat, and Zaki Bani Rsheid, chief of the political office of the Islamic Action Front (IAF).
Witnesses said the two men were "protected and evacuated by participants" when the violence began.
A rally by youths demanding political reforms held on Friday in the city of Irbid was similarly disrupted by unknown attackers, witnesses said.
Jordan has been the scene of protests since January to demand sweeping economic and political reform.
The NFR was formed in May by the Muslim Brotherhood, leftist parties, trade union leaders and independent figures. (*)
Editor: Kunto Wibisono
Copyright © ANTARA 2011
