NAJRAN, Saudi Arabia—A rocket fired from Yemen killed two girls Sunday in the Saudi Arabian border town of Najran, a Saudi civil defense official said, as Houthi rebels escalated their attacks after the collapse of political talks to end the 17-month conflict.

The attack, which also injured five other family members, came a day after a 3-year-old boy was killed and his 9-year-old cousin injured when a Katyusha rocket fired from Yemeni territory hit their home in the kingdom’s southern region, the official said.

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