It’s a nightmare scenario for Saudi Arabia, and it has sent jitters through global markets.

The Saudis’ most essential ally, the United States, has been unpredictableand sometimes unreliable. U.S. President Donald Trump seems reluctant to widen an already unpopular and stalemated Mideast war ahead of congressional elections. For Iran, the rebels’ advance and closure of the pipeline ramp up global economic pressure as its grip over the Strait of Hormuz has been loosened.

Michael Ratney, a former U.S. ambassador to Saudi Arabia, said the latest developments are “incredibly frustrating” for the kingdom.

“Despite their antipathy for the Iranians, this is a war they had never asked for, they had great trepidation about. And once it started, all of their … worst-case scenarios started coming true.”

The Saudi government did not respond to a request for comment. But a Saudi official, who was not authorized to brief media and spoke on condition of anonymity, said the kingdom would defend itself and work with partners, including the United States, to ensure freedom of navigation in the Red Sea.