A researcher for Human Rights Watch told The New York Times that police this week fired tear gas and used batons against demonstrators defying a government ban on protests.
Ennahda, the Islamist party that gained dominance in post-revolution Tunisia, was accused by members of the opposition of sending paramilitary forces into the streets to take on protesters.
Rachid al-Ghannouchi, co-founder of Ennahda, told al-Arabiya the allegations were baseless.
"We have no militias and I am warning against the fabrication of accusations without any proof and the division of Tunisian society along ideological lines," he said.
Political analysts told the Arab news service that while most Tunisians were united in their opposition to the former regime, political disputes are emerging as the country transitions to democracy.
Adel al-Shawsh, member of the communist Ettajdid Movement, told al-Arabiya a strong opposition was needed to counter Ennahda.
"The balance of power also needs to be changed and a moderate party that can counter the Islamist influence has to be established," he said.