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Hani Mohammed, Associated Press
Houthi Shiite rebels remove a tent that was erected two months ago, at a sit-in at a main road leading to the airport in Sanaa, Yemen, Friday, Oct. 17, 2014. Yemeni security officials say fierce clashes have erupted between Shiite rebels in control of the capital and tribesmen allied with the country's Islamist Islah party, leaving eight dead.

SANAA, Yemen — Yemen's empowered Shiite rebels attacked the home of a rival Islamist politician south of the capital on Saturday, setting off clashes that left 12 people dead, security officials said, adding that the politician was not home at the time.

The officials said Shiite rebels and allied fighters attacked the home of a local politician from the rival Islamist Islah party, killing two of his relatives in the town of Yarim, an Islamist stronghold in the Ibb province south of Sanaa. The ensuing clashes left eight rebel fighters and two bystanders dead.

Another four rebels were killed when a roadside bomb struck a convoy bringing reinforcements to a battle with Sunni conservative tribesmen raging in both Yarim and the provincial capital, also called Ibb. The Houthis had advanced on Ibb city on Friday, setting of fierce clashes. A brief cease-fire collapsed.

In a separate incident, officials said another eight people were killed in clashes between al-Qaida militants and the Houthis, who are fighting to maintain control of the city of Radaa, in the central province of Bayda, also south of the capital. The Houthis seized control of the city a day earlier. Scores of families fled the fighting in Radaa, which died down after midday Saturday.

All officials spoke on condition of anonymity because they were not authorized to speak to the media.

The Houthis gained control of the capital Sanaa in September, and earlier this week they overran a key Yemeni port city on the Red Sea. They have signed a peace agreement with the embattled central government to nominate a new Cabinet and end the fighting, but have simultaneously pressed their offensive, pushing their way into cities and towns south of the capital.

The rebels claim they are responding to calls by local residents who want them to drive out corrupt officials.

The Houthis are at loggerheads with the country's powerful Sunni tribes and the allied Islamist Islah party. The rebels are demanding a bigger share of power and a change to the country's political order following the 2011 protests that forced longtime leader Ali Abdullah Saleh out of office. Saleh's supporters have backed the Houthis' offensive.