The Philippine armed forces have launched a helicopter airstrike as part of their ongoing assault at Muslim rebels occupying parts of a major southern city, stepping up efforts to end an eight-day standoff that has left dozens dead. Two air force helicopters fired rocket rounds towards Moro National Liberation Front (MNLF) rebels held up in coastal villages in Zamboanga city on Monday, the military said. Al Jazeera's Jamela Alindogan reports from Zamboanga city, Philippine.