Pakistan, Sept. 9 -- Yemen's Tehran-backed Houthis attacked four cities in the south of Saudi Arabia on Tuesday, wounding more than 70 people and setting oil installations ablaze in what appeared to be a major expansion of the six-month-old Middle East war.

The Houthis, who control most of Yemen's populated areas including the capital, said they had launched a broad operation deep into Saudi territory. They used drones and missiles to strike a Saudi airbase in the southern city of Khamis Mushait, and targets belonging to Saudi Arabia's state oil company in nearby Abha, Najran on the Yemeni border, and Jazan, a major Red Sea port city that houses a large refinery and power plant.

NASA satellite images showed a thick cloud of black smoke ...