(Adds statement by local officials)
SANAA, Feb 28 (Reuters) - At least 13 people died when Shi'ite Muslim fighters clashed with security forces in northern Yemen on Friday, government sources said, underlining the chaos still gripping the country two years after mass protests ousted its leader.
The fighters were from the Houthi movement which is seeking to strengthen its hold on the north - one of a string of challenges facing an interim government also battling southern separatists, al Qaeda-linked militants and an economic crisis.
Local authorities said two soldiers were killed in the attack and four others were wounded when Houthis attacked a security checkpoint in the northwestern al Jawf province, according to state news agency Saba.
An exchange of fire took place as a result of the attack and three of the Houthi attackers were killed and several others were then arrested, a statement by the local authorities said.
The security situation in Yemen is closely watched in Gulf Arab states and Washington given the impoverished country's strategic position next to top oil exporter Saudi Arabia and to main shipping lanes.
Security sources had told Reuters violence erupted after members of the Houthi group staged a protest in al Hazm, the provincial capital of al Jawf province, against what they said was the government's failure to boost the economy and end violence.
Officials from both sides had given different accounts of what happened next.
One government security source, who asked not to be named, said armed Houthis exchanged fire with soldiers at an army checkpoint near a local government compound, leaving at least 10 Houthis and three soldiers dead.
Another security source said some of the soldiers may have been supporters of one of the Houthis' long-standing foes - the Sunni Islah party, a group linked to the Muslim Brotherhood.
The Houthis said they were attacked by armed Islah members supported by a group from the army, according to a statement on a Houthi-linked website.
There were "dozens of dead and wounded", Ali al-Bakhiti, a member of the Houthi movement in the capital Sanaa, told Reuters. Islah member Mohammed Qahtan said the group had no armed wing and played no part in Friday's fighting.
Yemen's interim President Abd-Rabbu Mansour Hadi has been struggling to restore order and meet the demands of the country's rival groups since his predecessor, veteran strongman Ali Abdullah Saleh, was forced out of office in 2012.
On Wednesday, the U.N. Security Council authorised sanctions against anyone in Yemen who obstructs the country's political transition or commits human rights violations but stopped short of blacklisting any specific individuals. (Reporting by Khaled Abdullah in Sanaa; Additional reporting and writing by Rania El Gamal in Dubai, editing by David Evans)