By AHMED AL-HAJ

    Quadruple suicide bombers on Friday hit a pair of mosques controlled by Shiite rebels in the Yemeni capital, Sanaa, unleashing blasts through crowds of worshippers that killed at least 137 people and wounded around 350 others in the deadliest violence to hit the fragile war-torn nation in decades.
    A group claiming to be a Yemeni branch of the Islamic State group said it carried out the attack and warned of an "upcoming flood" of attacks against the rebels, known as Houthis, who have taken over the capital and much of Yemen. The claim, posted online, could now immediately be independently confirmed and offered no proof of an Islamic State role.
    If true, Friday's bombing would be the first major attack by IS supporters in Yemen and an ominous sign that the influence of the group that holds much of Iraq and Syria has spread to this chaotic nation, where a powerful wing of the rival militant group al-Qaida already operates. The claim was posted on the same website in which the Islamic State affiliate in Libya claimed responsibility for Wednesday's deadly attack on a museum in Tunisia.
    The rebels, known as Houthis, have controlled the capital since September and have been locked in battle with Sunni al-Qaida fighters in various parts of the country. An official with al-Qaida in Yemen said his group was not behind Friday's attack.
    The four bombers attacked the Badr and al-Hashoosh mosques, located across town from each other, during midday Friday prayers, traditionally the most crowded time of the week, according to the state news agency. Both mosques are controlled by the Shiite Houthis, but they also are frequented by Sunni worshippers.
    The rebel-owned Al-Masirah TV channel said the casualty figures had reached 137 dead and 345 injured and reported that hospitals were urging citizens to donate blood. It also reported that a fifth suicide bomb attack on another mosque was foiled in the northern city of Saada - a Houthi stronghold.