How did the militants get control of the Red Mosque? Maulana Abdul Aziz and his younger brother, Abdul Rashid Ghazi, inherited the mosque and madrasah complex when their father, Maulana Abdullah, was assassinated in the late 1990s. The government says his sons stole adjacent state-owned land to expand their empire soon afterwards.
Where do the children in the mosque come from? Most are from poor, conservative families in the North West Frontier province and Waziristan who are attracted by the free board and religious education. Others come from as far as Skardu in the north and Kashmir. Some 500 children entered the mosque when orphaned by the 2005 earthquake.
Have they been trained as suicide bombers? There is no firm evidence that children are being trained as suicide bombers, but strong indications they are being prepared for the idea of martyrdom. Some, says the government, are being held as human shields.
Why has President Pervez Musharraf taken so long to clamp down? He has been paralysed by the fear of bloodshed in the shadow of his own presidential palace and before the world's 24-hour news channels.
Is there support for the militants in Pakistan? There has been a wave of suicide bombings in Waziristan and the North West Frontier to protest against the crackdown. But the militants enjoy little backing in cities and there have been demonstrations against calls to introduce sharia (Islamic law).
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What lies behind their campaign to impose a strict Islamic rule in Islamabad? The clerics and their followers say it is to prevent "vice" by confronting those engaged in the sex trade. Officials believe their real agenda is to hang on to land they have stolen.
Could there be a bloodbath? There could, and this is what alarms officials more than anything else. If Ghazi, the de facto leader, chooses martyrdom rather than surrender, hundreds of women and children could be at risk.
How will the crisis affect elections later this year? A massacre would jeopardise Musharraf's chances. If the siege ends relatively peacefully, it will boost his standing with many voters.