Since 2004, the Yemeni government has been intermittently fighting a Zaidi (Shia) rebellion based in Saada province in the north of the country, adjacent to the Saudi border. 

The most recent outbreak occurred in August 2009 when the government launched "Operation Scorched Earth" against the rebels. That phase of the conflict ended in February 2010 when both sides agreed a ceasefire.

There was little first-hand reporting of the conflict because of media exclusion from the area. The scale of casualties is unknown but many thousands of people fled their homes, resulting in a serious humanitarian crisis.

The following reports and articles provide useful background on the conflict:

Sa'dah insurgency 
Wikipedia

Yemen: Defusing the Saada Time Bomb  
International Crisis Group, May 2009

Yemen: Fear of Failure 
by Ginny Hill. Chatham House Briefing Paper, November 2008

The conflict in Saada governorate 
UN Office for the Coordination of Humanitarian Affairs, July 2008

Media absent from Yemen’s forgotten war 
by Maysaa Shuja al-Deen. Arab Media & Society, Spring 2009

Conflict in Saada 
Middle East International, 9 July 2004

Northern Yemen Emergency
UNHCR factsheet, 3 September 2009
(Note: the factsheet incorrectly refers to 100,000-150,000 displaced people in the Saudi border areas. The UNHCR later corrected this: it should say 100-150 families.)

Humanitarian crisis in northern Yemen intensifying, UN cautions 
UN News Centre, 4 September 2009