May 12 (Reuters) - Sudan has accused neighbouring Chad of backing rebels who attacked the capital Khartoum at the weekend and has cut diplomatic relations.

Here is a chronology of recent Chad-Sudan tensions:

Jan/Feb 2004 - Thousands of refugees from Sudan's Darfur region arrive in Chad fleeing government bombings and raids by Arab Janjaweed militias.

April 9 - Chad brokers a ceasefire between the Sudanese government and two Darfur rebel groups.

April 11, 2005 - Chad suspends mediation, accusing Sudan of supporting Chadian rebels. It returns to mediation after promises from Khartoum that it would act against the rebels.

Dec. 18 - Chad says its forces killed about 300 rebels after they launched a failed offensive on the border town of Adre. Sudan denies involvement.

Feb 8, 2006 - Chad and Sudan agree to put an end to their dispute at a meeting in Libya.

April 13 - Chad government forces fight off attack by rebels on the capital N'Djamena. Several hundred people killed. Deby breaks diplomatic relations with Sudan the next day.

Aug 8 - Chadian President Idriss Deby and Sudanese President Omar Hassan al-Bashir agree to restore ties.

Feb 1, 2007 - Rebels fighting to overthrow Deby launch an attack on Adre, before being beaten back.

Feb 22 - At a conference in Libya, leaders of Sudan and Chad pledge to redouble efforts to end border violence.

May 3 - Sudan and Chad sign a Saudi-brokered reconciliation deal in Riyadh.

Oct 25 - Chad and four Sudan-based Chadian rebel groups sign a "definitive peace accord" in Libya. At least two groups later abandoned the accord.

Feb 3, 2008 - Deby beats back rebels who got as far as the presidential palace in an attempt to oust him. Former colonial power France rallies behind Deby.

March 13 - Sudanese and Chadian leaders sign non-aggression deal in Senegal however Chadian rebels dismiss the peace pact the next day.

May 10 - Rebels make a lightning advance from the western Darfur region to attack Khartoum. About 65 people are believed to have been killed in the attacks.

May 11 - Sudan accuses Chad of backing the rebels and cuts diplomatic relations. Chad denies involvement.

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