FACTBOX - The battle against militancy in South Waziristan

ISLAMABAD (Reuters) - Missile strikes by a suspected U.S. drone aircraft on Monday killed at least 17 militants in Pakistan's South Waziristan, intelligence officials said, following reports that a top al Qaeda operative was killed in the region last week.

Monday's drone attack near the Afghan border, the biggest since March, may signal that the CIA identified high-value al Qaeda or Taliban targets in South Waziristan. Drone missile strikes usually focus on North Waziristan.

A Pakistani security official said he believed the drone strikes have escalated in South Waziristan because speculation that the Pakistani army planned to mount an offensive in North Waziristan prompted militants to head south.

Here are some facts about South Waziristan:

* South Waziristan is one of seven tribal agencies in the northwest in a region seen as a global hub for militants. Forbidding terrain makes the region and ideal spot for militants to train and plot attacks. Foreign fighter also operate in South Waziristan so the United States may have picked up information suggesting some high-profile Arab al Qaeda militants are present in the region.

* 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, Khyber Pukhtunkwa province to the east and Baluchistan province to the south. The main town in the region is Wana.

* Arid and mountainous, South Waziristan's rugged terrain is pock-marked with sparse forest and dried-up creeks, with some important industry and agriculture taking place on the vast and rocky plains around Wana.

* The latest drone strikes in South Waziristan were in an area controlled by Pakistani Taliban commander Maulvi Nazir.

He is one of the so called "good Taliban" -- fighters who are not opposed to the Pakistani state and focus on crossing the border and attacking U.S.-led NATO forces in Afghanistan.

The United States wants Pakistan to go after such militants but the Islamabad government has been reluctant.

* South Waziristan has an estimated population of about 500,000, according to the most recent figures, mostly ethnic Pashtuns. Generally regarded as religious conservatives and with a reputation for being fiercely independent and hostile to outside interference, Pashtuns are also hospitable and protective of visitors. So persuading them to go after or hand over militants can be a daunting task.

The Pashtuns are divided into tribes, with the main ones in South Waziristan being the Mehsuds -- from whom the Pakistani Taliban draw much support -- and the Wazirs. Tribes are further sub-divided into clans.

* South Waziristan's main militant bastion is a wedge of territory in a Mehsud tribal region which does not border Afghanistan. The army has launched offensives against militants in South Waziristan, the last taking place in 2009, forcing many Taliban fighters to flee to North Waziristan.

* Drone strikes in South Waziristan have fallen off in frequency over the past year.

The attacks have come into sharper focus since Pakistani officials said senior al Qaeda operative Ilyas Kashmiri was killed in a drone strike not far from the latest attacks in South Waziristan, late on Friday.

National Security officials in Washington expressed serious doubts about reports of his death.

(Editing by Michael Georgy and Sanjeev Miglani)