SANAA, Jan 12 (Reuters) - At least four fighters from a Sunni Salafi Islamist group were killed in heavy clashes in northern Yemen on Thursday with Shi'ite rebel fighters, a spokesman for the Islamist group said.
Both sides blamed each other for the bloodshed on the border with the world's biggest oil exporter and main regional U.S. ally, Saudi Arabia.
The clashes were the latest flareup in one of the internal conflicts threatening a power transfer deal signed in November last year to pull back Yemen from the brink of civil war.
Surour al-Wadi'i, a spokesman for the Salafis -- Sunnis who espouse a puritanical creed with many followers in Saudi Arabia -- said Houthi fighters attacked early on Thursday in an area near the city of Saada north of the capital Sanaa.
The Salafis beat back the Houthis with automatic weapons and "four brothers were martyred", Wadi'i said.
A statement issued by the Shi'ite group's leader, Abdelmalek al-Houthi, accused the Salafis of waging "unjustified aggression" against residents of the area of Ahem, saying attacks began on Wednesday when one person was killed in the area.
Dayfallah al-Shami, a member of the Houthis' political leadership council, said there were casualties in fighting with Salafis in the area on Thursday but gave no details.
OPPONENTS OF SALEH GIVEN DEADLINE
The fighting came as a military committee responsible for demilitarising the capital gave armed opponents and backers of outgoing President Ali Abdullah Saleh 48 hours to begin withdrawing after months of street fighting.
The presence of armed elements in Sanaa, defying an earlier deadline to leave their positions by the end of December, underlines the difficulty of restoring normality to the country, which was paralysed for most of 2011 by protests against Saleh.
The peace accord must also pass another hurdle involving getting parliament to pass a draft law granting Saleh and his family immunity from prosecution for any action committed during Saleh's 33 years in office.
An immunity bill has been approved by the cabinet, despite street protests against granting Saleh immunity. But some ministers continue to express opposition to giving Saleh immunity, hampering the convening of parliament.
U.N. envoy Jamal Benomar, who helped broker the power transfer deal, drafted by the six-member Gulf Cooperation Council, in November returned to Yemen on Thursday to follow up on implementation of the accord, Yemeni officials said.
Analysts say Saleh was expected to leave Yemen for treatment abroad after parliament approves the immunity bill, allowing Yemenis to start preparations for presidential elections set for Feb. 21.
(Reporting by Mohammed Ghobari, writing by Sami Aboudi)