* Yemen dogged by sectarian fighting
* Sunnis, Shi'ite rebels trying to implement ceasefire
SANAA, Jan 20 (Reuters) - At least 12 people were killed in northern Yemen overnight after Sunni Muslim tribesmen fought with a Shi'ite group which was trying to capture a mountain, tribal sources said on Monday.
The fighting in Yemen's Omran province is the latest in a series of deadly confrontations in the north between Shi'ite Houthis and their Sunni rivals, who include local tribes and Salafi Islamists.
Months of intense sectarian fighting have cast a shadow over national reconciliation efforts in Yemen, a neighbour of major oil exporter Saudi Arabia and home to one of al Qaeda's most active wings.
Eight Houthis and four members of the pro-Salafi Al Ahmar clan were killed late on Sunday after the Shi'ite rebels tried to seize the mountain, the local Sunni tribal sources said.
It was not immediately possible to independently confirm the clashes.
The two sides have been trying to implement a ceasefire agreed earlier this month, under which the Salafis have relocated to the Red Sea port city of Hudaida, more than 250 km (155 miles) away.
While the ceasefire was largely holding across most of northern Yemen, clashes have continued in more remote areas in Omran, where fighters are trying to gain control of territory, the sources added.
The adjacent Saada province is the base for a long-running Houthi uprising against the Yemeni government in Sanaa, which the rebels say discriminates against them.
The Sunni-Shi'ite conflict has compounded the challenges facing Yemen, a U.S. ally and the poorest Arab country.
It is also struggling with a separatist movement in the south, where mainly Islamist militants took advantage of a popular uprising in 2011 to strengthen their hold on some areas. (Reporting by Mohammed Ghobari, Writing by Sylvia Westall; editing by Sami Aboudi and Gareth Jones)