FACTBOX: The battle in Pakistan's South Waziristan

(Reuters) - Pakistani forces backed by heavy artillery attacked Taliban insurgents on Thursday as the army moved to wrest control of militant strongholds in a lawless region on the Afghan border.

(For a graphic showing the whereabouts of fighting, see here)

The military launched the offensive in South Waziristan on Saturday after several months of preparation and following a string of brazen militant attacks including one on the army headquarters this month.

Here are some facts about South Waziristan:

THE LAND

South Waziristan has an area of about 6,620 square km (2,550 square miles). It borders Afghanistan to the west, North Waziristan to the north, North West Frontier Province to the east and Baluchistan province to the south. Its main town is Wana. It is an arid land of mountains pocked by dried-up creeks, along with sparse forests and rocky plains.

THE PEOPLE South Waziristan has an estimated population of about 500,000, according to the most recent figures, mostly ethnic Pashtuns. Pashtuns in general are religious conservatives and have a reputation for being fiercely independent and hostile to outside interference, but are also hospitable and protective of visitors. The Pashtuns are divided into tribes, with the main ones in South Waziristan being the Mehsuds -- from whom the Taliban draw much support -- and the Wazirs. Tribes are further sub-divided into clans. THE FIGHTING

The main Pakistani Taliban bastion is a wedge of territory in a Mehsud tribal region. The heartland does not border Afghanistan.

The army has launched brief offensives there before, the first in 2004 when it suffered heavy casualties before striking a peace pact. This time, the army has spent months preparing and it says it has encircled the main Pakistani Taliban zone.

The army says about 28,000 soldiers are in place to take on an estimated 10,000 hard-core Taliban. The Taliban forces include about 1,000 Uzbek militants, who have a reputation for being ruthless fighters, some al Qaeda Arabs and even a handful of militants from Western countries.

The army is attacking from three directions, with ground troops backed by jets, helicopters, tanks and artillery.

The militants have had years to prepare their defenses and hold rifles, machineguns, anti-tank weapons, especially rocket-propelled grenades, mortars and longer-range rockets.

They are also experts in the use of roadside bombs and have been churning out a stream of suicide bombers.

The United States has also been attacking the militants with missile-firing drone aircraft even though Pakistan officially objects to the strikes. Pakistani Taliban leader Baitullah Mehsud was killed in a missile strike on August 5. His successor has vowed revenge.

The army has been trying to isolate the Pakistani Taliban in their stronghold and will be hoping other militant factions, including a Wazir-dominated faction led by commander Maulvi Nazir in South Waziristan, and other factions, will stay out of the battle.

(Editing by David Fox)