Factbox: Roots of Yemen's conflict with northern rebels

(Reuters) - Yemen's Shi'ite rebels on Monday offered Saudi Arabia a truce and said they would withdraw from its territory as the cost to civilians was too high.

Yemen has been battling the intermittent revolt since 2004. The fighting intensified in August when the army launched Operation Scorched Earth. The conflict drew in Saudi Arabia in November when the rebels seized some territory on its border.

The rebels, known as the Houthis after the family name of their leader Abdul-Malik al-Houthi, are fighting government troops in the north, complaining of social, religious and economic discrimination.

Here is some background about the Houthi rebels:

WHO ARE THE HOUTHIS?

* The Houthis, like most tribesmen in Yemen's northern highlands, belong to the Zaidi sect of Shi'ite Islam, whose Hashemite line ruled for 1,000 years before the 1962 revolution.

* Zaidis, who make up about a third of Yemen's 23 million people, have coexisted easily with majority Sunnis in the past, but Badr al-Din al-Houthi, a cleric from the northern province of Saada, promoted Zaidi revivalism in the 1970s, playing on fears that Saudi-influenced Salafis threatened Zaidi identity.

* After north and south Yemen united in 1990, the movement spawned the al-Haq party and the Houthi-led Believing Youth group. Houthi's son Hussein was elected to parliament in 1993. Saada remained neglected economically by the Sanaa government.

* President Ali Abdullah Saleh, himself a Zaidi, at first used the Houthis to counter-balance the Salafi groups. The government later portrayed Believing Youth as a fundamentalist group out to subvert the state and restore the Zaidi imamate.

* After the September 11, 2001 attacks on U.S. cities, Saleh declared support for Washington's "war on terror," in part to enlist U.S. support against the Houthis, whom Yemeni officials accuse of having links to al Qaeda, Iran or Lebanon's Hezbollah.

* The Houthis say the government, with U.S. and Saudi backing, is targeting Zaidis in general, forcing them to take up arms to defend their villages against oppression.

CONFLICT BEGINS:

* Conflict began after Houthis embarrassed Saleh by shouting "Death to America, death to Israel, a curse on the Jews, victory to Islam" in his presence in a Saada mosque in 2003.

* Security forces killed Hussein al-Houthi in September 2004, only to see further rounds of fighting erupt in the mountains around Saada city, each more violent than the last.

* Qatar brokered a ceasefire in June 2007 and sponsored a peace deal signed in February 2008, but clashes soon resumed. Saleh unilaterally declared the war over in July 2008. Full-scale fighting resumed a year later.

A SAUDI OFFENSIVE:

* In November, Saudi Arabia launched a military offensive against the rebels after a rebel cross-border incursion. Houthi denied accusations that infiltrators entered Saudi territory and called the offensive against the group "unjustified" and accused it of mainly targeting civilians through air raids.

* Saudi Arabia claimed victory on December 26, saying the army had driven the last infiltrators from its territory, an Arabic language daily said. Rebels have reported that Saudi air strikes on the Yemen-Saudi border were continuing.

Sources: Reuters/International Crisis Group

(Writing by Alistair Lyon and David Cutler, London Editorial Reference Unit; Editing by Janet Lawrence)