The civilian death toll from the fighting and airstrikes since the bombing started on March 26 has reached an estimated 551 people, the United Nations said on Friday. Its children’s agency UNICEF said at least 115 children were among the dead.

Washington and other Western countries backing the Saudi-led aerial campaign have grown increasingly worried about the humanitarian crisis on the ground and also about the risk of Sunni Muslim jihadist groups taking advantage of the chaos.

Islamic State, which has had little presence in Yemen, released late on Thursday a video it said showed members of the group in the country conducting military exercises and pledging to attack the Houthis, who are from the Zaydi Shi’ite sect.

Saudi Arabia has called a meeting with major U.N. aid agencies and others to discuss improving aid deliveries to Yemen, which have been hindered by the naval blockade, Saudi officials and U.N. sources said.

Violent clashes continued between the Houthis and local militias near the Khor Maksar district of Aden on Friday, residents said, as well as in Taiz and al-Dhala.

Heavy fighting in Marib province east of the Yemeni capital Sanaa killed 15 people, tribal sources there said, as the Houthi militia and forces loyal to former president Ali Abdullah Saleh tried to advance into the rugged Sirwah district.

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