Iran's allies are gaining strength on Saudi Arabia's borders, creating the worst security environment for the kingdom in decades.  

Saudi Deputy Prime Minister and Minister of Interior Mohammed bin Nayef summoned his Gulf Cooperation Council (GCC) counterparts to Riyadh over the weekend to address the rapidly deteriorating situation in Yemen, where pro-Iranian Zaydi Shiite Houthi rebels are advancing on the remnants of President Abed Rabbo Mansour Hadi's Sunni government. Abu Dhabi Crown Prince Sheikh Mohammed bin Zayid, Bahraini Crown Prince Salman bin Hamad Al Khalifah and their Qatari and Kuwaiti colleagues attended the GCC meeting and also met with King Salman bin Abdul-Aziz Al Saud in his royal palace in Diriyah outside Riyadh. The king and his visitors warned that Yemen was slipping into "a dark tunnel" with bad consequences for the entire region.

Notably absent was Oman, Yemen's closest neighbor. The sultan had been absent from Oman for medical reasons in Munich and apparently did not choose to send a ranking representative to the GCC meeting. He has no heir appointed, which leaves decision-making difficult. Oman is also somewhat more relaxed about Iranian actions than its Gulf allies.

The Zaydi rebel army on March 22 seized much of Taiz, Yemen's third-largest city and the gateway to south Yemen and Aden, where Hadi is trying to rally Sunni opposition to the Houthis. The Houthis are also benefiting from increasingly overt support from forces loyal to former President Ali Abdullah Saleh, who still has influence in the Yemeni military.