Ten people were killed in north Yemen Saturday when Shi'ite Muslim rebels shelled positions held by Sunni Islamist Salafi fighters after the collapse of a week-old cease-fire, a Salafi spokesman said.

The conflict between the Shi'ite Houthi rebels and the Sunni Salafis is just one of several plaguing Yemen as the country looks to elections to replace President Ali Abdullah Saleh, who agreed this week to step down after 10 months of protests to end his 33-year rule.

In recent weeks, the Houthis have skirmished with Salafist fighters, leading local tribesmen to broker a truce between them a week ago.

The Houthis broke the cease-fire and shelled the town of Damaj, said the Salafi spokesman, who identified himself as Abu Ismail, adding 15 people were injured.

The fresh violence highlights the risk of civil war in a country that borders the world's largest oil exporter, Saudi Arabia. Washington and Riyadh fear a political vacuum in Yemen could embolden al Qaeda's Yemen wing and potentially threaten oil supplies.

Members of the Zaidi sect of Shi'ite Islam, the Houthi rebels led an uprising based in the northern Saada province that Saleh's forces have struggled to crush, with Saudi Arabia intervening militarily in 2009 before a cease-fire took hold the following year.

The Houthis, who effectively control Saada, are deeply wary of Saudi Arabia's promotion of puritanical Sunni Salafi creeds that regard Shi'ites as heretics.

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Saleh Habra, a Houthi leader, has accused the Yemeni government of supplying arms to the Salafis, who he said were trying to build a military camp near the Saudi border, and said his side was trying to keep arms from reaching their enemies.

We are trying to cut off their arms supplies, Habra told Reuters last week.

Separately, Yemeni combat aircraft bombed sites used by anti-government tribal militants in northern Sanaa, killing seven people, tribal sources said Saturday.

Those sources said tribal fighters were seeking to surround a camp used by the Republican Guard, a unit led by Saleh's son.

(Reporting by Mohammed Ghobari; Writing by Mahmoud Habboush; Editing by Sophie Hares)