The Gaza-based Salafist group Jaysh al-Umma accused the ruling Hamas movement on Monday of arresting and torturing six of its members, including its leader.
In a statement obtained by AFP, the group said it was breaking the "media blackout" over the arrest of its leader Sheikh Ismail Hamid, also known as Abu Hafs al-Maqdisi.
He is "languishing in the dark cells of the Hamas government, subjected to harsh interrogation," the group said, adding that five other members were also being held by Hamas forces.
"There will be no compromises, the Sheikh will continue jihad and preaching and will not be subject to political calculations that waste our rights and embolden our enemies," the group said.
The statement said Ismail had been arrested at gunpoint during the fasting month of Ramadan and was being subjected to "physical and psychological torture."
"The charges against him are jihad for the sake of God, and his links to the firing of rockets at Jewish settlements, as well as a campaign in Gaza warning about Shiites and their beliefs," the statement said.
The Hamas government has found itself at odds with an array of small jihadist, Salafist groups operating in the Gaza Strip, which have challenged the Islamist movement both over confrontations with Israel and the practice of Islamic rule in Gaza.
Hamas maintains a tacit truce with Israel, calling on militant groups, including its own military wing, to avoid firing rockets into the Jewish state.
But the Salafist groups have regularly breached the truce, and accuse Hamas of collaborating with Israel by maintaining the unwritten quiet.
The groups have also challenged Hamas inside Gaza, accusing the ruling movement of failing to implement a strict enough interpretation of Islamic law.