New Delhi, Oct. 7 -- The Houthis have responded by escalating missile and drone attacks on Saudi Arabia, claiming to have struck the international airport in the capital, Riyadh, an Aramco refinery and Saudi military bases. They have also advanced around a city in western Yemen that has been a major battleground in the 12-year civil war.

The worst fighting in Yemen in years comes as tensions remain high between the U.S. and Iran.

The U.S. and Gulf nations have largely restored oil exports despite Iran's monthslong disruption of the Strait of Hormuz. But U.S. President Donald Trump has warned he might resume full-scale military operations after the U.S. congressional elections in November, and Iran could be planning proxy attacks.

The p...