Saudi Arabian warplanes pounded Houthi rebels overnight in an effort to stop their advance on southern Yemen. The Saudis and nine other allies launched airstrikes Wednesday after the Shiite militants captured airstrips around the southern port city of Aden, and fired on the residence of President Abd Rabbuh Mansur Hadi.
The embattled president had fled the palace ahead of the rebel advance; it's unclear where he is.
The U.S. said late Wednesday that it is providing logistical and intelligence support to the military effort by Yemen's allies.
Shiite Iran, which backs the Houthis, called the operation "dangerous" and likened it to an invasion. NPR's Deborah Amos reports that Iran complained that the air campaign against the rebels was a U.S.-backed operation.
The Guardian reports that the Al-Arabiya news channel said Saudi Arabia had lined up 150,000 soldiers in preparation for a ground offensive, and that Egypt, Pakistan, Sudan and Jordan were prepared to commit troops.
The increasing chaos in Yemen could set up a new front between the Middle East's Sunni powers and Shi'ite Iran. The New York Times reports that the Saudi Arabian intervention in Yemen immediately raised the threat that Iran might retaliate by increasing its own support for the Houthis with weapons and money.
Its members are anti-U.S., but are also battling al-Qaida in the Arabian Peninsula. They are also likely to take on the self-described Islamic State. Both AQAP and ISIS are Sunni and regard Shiites as heretics.
As NPR reported Wednesday: "The ongoing volatile political and security situation has forced the U.S. to pull all its remaining personnel — civilian, military and intelligence — out of the country. The move could have an impact on U.S counter-terrorism efforts against al-Qaida in the Arabian Peninsula, considered one of the most dangerous offshoots of the terror group."
The escalating tensions in the Middle East have sparked a modest rise in oil prices, according to Reuters news agency. Yemen has a coastline on the Bab el-Mandeb Strait, which connects the Red Sea with the Gulf of Aden and the Arabian Sea. The news agency says on average almost 4 million barrels of oil pass through the Strait every day.