Dec 3 (Reuters) - Congo's army attacked a stronghold of renegade Tutsi General Laurent Nkunda on Monday, a day after his men took a strategic town from the government and forced out thousands of civilians, U.N. and army officials said.

The army shelled rebel positions around Mushake, 40 km (25 miles) west of North Kivu's provincial capital Goma.

Nkunda and his fighters have been battling with the United Nations-backed Congolese army in North Kivu province, forcing thousands of civilian refugees to flee their homes.

Here are some details about the fighting in the east.

* ORIGINS OF THE CONFLICT:

-- The roots of Nkunda's rebellion in North Kivu lie in unhealed ethnic and political wounds that have made the racially mixed eastern Congo a regional tinderbox.

-- The presence of both Tutsi and Hutu rebels there stems from Rwanda's 1994 genocide. The genocide saw 800,000 Tutsis and moderate Hutus killed in 100 days by the Hutu-led government and ethnic militias.

-- It led to subsequent invasions by Rwandan forces that helped ignite the 1998-2003 war in Congo.

-- Nkunda led a revolt in 2004 with around 4,000 soldiers and briefly captured Bukavu, the capital of South Kivu. He still faces an international arrest warrant for war crimes allegedly committed during the brief occupation.

-- Following 2006 elections aimed at drawing a line under the 1998-2003 war which killed some 4 million people, President Joseph Kabila promised to bring peace to Congo's east.

-- However in a November 2006 crackdown, United Nations Mission in Congo (MONUC) helicopters and armoured vehicles killed hundreds of Nkunda's fighters.

-- Under a January, 2007 peace deal Nkunda's fighters joined special mixed army brigades, but walked out again in August.

-- Nkunda says he is fighting to protect his Tutsi people in eastern Congo against attacks by the Democratic Forces for the Liberation of Rwanda (FDLR) which control parts of North Kivu and which he says are backed by Kabila's government. The FDLR includes former Rwandan soldiers and members of Hutu militias, or Interahamwe, which took part in the Rwandan genocide.

* CEASEFIRE NOW OVER:

-- U.N. mediators announced a limited ceasefire on Sept. 6 after nearly two weeks of fighting in the volatile province as thousands of Tutsi fighters loyal to Nkunda appeared to have turned the tide on government forces, and were pressing ahead towards the provincial capital Goma.

-- Nkunda, who has turned much of North Kivu province into his personal fiefdom, has said he abandoned the ceasefire, because of attacks by the government, which in turn accused him of pushing the country towards war.

-- Last month, MONUC said all means of peacefully resolving the North Kivu crisis had been exhausted and it was preparing to help the army force Nkunda and his men to surrender.

-- Jendayi Frazer, U.S. assistant secretary of state for African affairs, said on Nov. 30 the best solution would be for Nkunda to go into exile. (Writing by David Cutler, London Editorial Reference Unit)

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