ANDIZHAN, Uzbekistan (Reuters) - Uzbek troops kill hundreds of people in Andizhan after an uprising in the mostly Muslim Central Asian state.

Andizhan lies in the heart of the volatile and fertile Ferghana valley. Here are five facts about the valley:

- The Ferghana valley's seven million inhabitants make it the most densely populated region of Central Asia. It has suffered ethnic violence and unrest since Soviet times. Clashes that killed dozens drove the Meskhetian Turk minority out of the region in 1989, while Kyrgyz and Uzbeks battled over land rights at the same time.

- Uzbekistan's secular government says the valley is a hothouse of Muslim extremists aiming to set up an Islamic state in the region. The government has locked up thousands of suspected militants, drawing sharp criticism from rights groups.

- The valley is largely ethnically Uzbek but is split between Uzbekistan, Tajikistan and Kyrgyzstan in a confused patchwork of Soviet-era borders which often leave enclaves of one country surrounded by the territory of another. In general, Uzbekistan holds the valley floor, Tajikistan holds its narrow mouth and Kyrgyzstan holds the high ground around.

- The valley mouth is narrow, but the actual valley is vast at 22,000 sq km (8,500 sq miles) and the Pamir and Tien Shan mountains that rise above are only dimly visible.

- The valley is a major centre of cotton and silk production, and the hills above are covered by walnut forests. The valley also has some oil and gas.