RFE/RL's Turkmen Service reports that the joint appeal was issued in Prague today following a meeting by representatives of the Social and Political Movement of Watan and the Turkmenistan Republican Party.
In the appeal, the parties accuse Niyazov of plundering the country's natural resources and destroying education, health care, and the justice system.
They call on Turkmen citizens to unite and do whatever they can to resist Niyazov's regime.
Normuhammad Khanamov, the exiled leader of the Republican Party of Turkmenistan, told RFE/RL the current conditions are untenable.
"The situation of the people is getting worse, to the extent that people can no longer bear it," he said. "To avoid such problems, some measures need to be taken. People and the opposition should do something together, to be able change this situation."
The Turkmen oppposition parties say they plan to write an appeal to the U.S. Congress.