Pakistani soldiers closed in on Tuesday on a Taliban headquarters in Swat, the military said, as the United Nations called for help for hundreds of thousands of people displaced by the fighting.
The offensive in Swat, 130 km (80 miles) northwest of Islamabad, is seen as a test of the government's commitment to face up to a growing Taliban insurgency and comes after the United States accused it of "abdicating" to the militants.
Here are some facts about Swat and the insurgency there.
* Swat is not on the Afghan border but Western countries with troops in Afghanistan fear the area could turn into a bastion for Taliban militants fighting in both Afghanistan and Pakistan and for al Qaeda.
* Islamist militancy emerged in Swat, an alpine beauty spot and former tourism 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, 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 gained control of almost the entire valley and unleashed a reign of terror, killing and beheading politicians, singers, soldiers and opponents. They banned female education and destroyed nearly 200 girls' schools.
* 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 a ceasefire after the army said it was halting operations. President Asif Ali Zardari signed a regulation imposing Islamic law 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.
* Taliban seized government buildings in Mingora, the main town in Swat, and the military began attacking them.
* Last Thursday, the prime minister directed the military "to eliminate the militants and terrorists" and the army stepped up its attacks the next day.
* Interior Ministry chief Rehman Malik said on Monday 700 Taliban and 20 soldiers had been killed. Most reporters have left Swat and there was no independent confirmation of that estimate of militant casualties, which was higher than figures provided by the military.
(Editing by Robert Birsel)