The Popular Front for the Liberation of Palestine (PFLP) on Tuesday said its patience was running out and would not accept the renewal of a ceasefire with Israel.
"We won't allow the continuation of the lull," said Rabah Muhana, a PFLP leader in the Gaza Strip. "From the beginning, the calmness was a mistake and our patience is running out."
The PFLP and several other factions reluctantly accepted the Egyptian-brokered ceasefire, which went into force in the Gaza Strip in June.
Hamas, which controls the coastal strip, has been negotiating with Israel via Egypt to reinforce the six-month ceasefire.
Muhana called on Abu Ali Mustafa brigades, PFLP's military wing, "to stay on full alert and be ready to pull the trigger" as the ceasefire may collapse at any time.
The unwritten agreement was designated to ease the blockade which Israel imposed on Gaza after Hamas seized rein of the impoverished enclave from Fatah-dominated security forces loyal to President Mahmoud Abbas last year.
But Hamas said Israel was not committed to the deal despite the halt of cross-border violence against the Jewish state.