FACTBOX - Conflict in Pakistan's Swat

May 9 - Pakistani helicopter gunships blasted Taliban positions in the militants' Swat valley bastion on Saturday, as a curfew blocked residents from joining hundreds of thousands who have already fled the fighting.

The struggle in the scenic northwestern valley 130 km (80 miles) from Islamabad and a former tourism center has become a test of nuclear-armed Pakistan's resolve to fight a growing Taliban insurgency that has alarmed the United States.

Pakistan's army went on a full-scale offensive on Friday after a government go-ahead to flush out violent militants from the Islamist stronghold, and the military said late in the day 143 militants had been killed over the previous 24 hours.

Here are some facts about Swat and the insurgency there.

* Swat, about 130 km (80 miles) northwest of Islamabad, is not on the Afghan border. Nevertheless Western countries with troops in Afghanistan fear the area could turn into a base for militants fighting in both Afghanistan and Pakistan.

* Islamist militancy emerged in Swat, an alpine beauty spot and former tourist favorite, in the 1990s when cleric Sufi Mohammad took up arms to impose sharia law there and in neighboring areas of the Malakand region.

* Mohammad was arrested after he returned to Pakistan having led thousands of fighters to Afghanistan in 2001 in a vain attempt to help the Taliban resist U.S.-backed forces.

* Pakistani authorities released him in 2008 in a bid to defuse another uprising, led by his son-in-law cleric Fazlullah, who has ties with other Pakistani Taliban factions and al Qaeda.

* Fazlullah called his men to arms after a military assault on the Red Mosque in Islamabad in mid-2007 to put down an armed movement seeking to impose Islamic law. Fazlullah used illegal FM radio to propagate his message and became known as Mullah Radio.

* The army deployed troops in Swat in October 2007 and used artillery and gunship helicopters to reassert control. But insecurity mounted after a civilian government came to power last year and tried to reach a negotiated settlement.

* A peace accord fell apart in May 2008. After that hundreds, including soldiers, militants and civilians, died in battles.

* Militants unleashed a reign of terror, killing and beheading politicians, singers, soldiers and opponents. They banned female education and destroyed nearly 200 girls' schools.

* About 1,200 people were killed since late 2007 and 250,000 to 500,000 fled, leaving the militants in virtual control.

* Pakistan offered in February to introduce Islamic law in Swat and nearby areas in a bid to take the steam out of the insurgency. The militants announced an indefinite ceasefire after the army said it was halting operations in the region. President Asif Ali Zardari signed a regulation imposing sharia in the area last month.

* But the Taliban refused to give up their guns and pushed into Buner, only 100 km (60 miles) northwest of Islamabad, and another district adjacent to Swat.

* Amid mounting concern at home and abroad, security forces launched an offensive to expel militants from Buner and another district near Swat on April 26.

* A Taliban spokesman said this week the peace pact would end unless the government halted its offensive in Buner, but it continued and the government then moved against Taliban positions within Swat itself.

* On Thursday the Prime Minister directed the military "to eliminate the militants and terrorists," and on Friday it launched fresh operations in Swat.

(Editing by Robert Birsel and Jerry Norton)