Discussions within the administration, and between Washington and Riyadh, continued this week as the U.S. considered how many troops to send to Saudi Arabia. The assessment comes in the wake of Iran’s attack on its oil facilities, and how those troops should be deployed.

Al-Arabiya reported on Thursday that Saudi Crown Prince Mohammed bin Salman (MBS), who among his many other titles serves as the kingdom’s defense minister, spoke with U.S. Secretary of Defense Mark Esper about arrangements to bring more American troops into Saudi Arabia:

Prince Mohammed bin Salman told Mark Esper that recent attacks on Aramco oil facilities were “a dangerous escalation for the whole world that requires a firm stand to preserve international peace and security,” SPA said. The US Secretary of Defense affirmed that the United States will do everything necessary to help the Kingdom to defend itself. Esper stressed that Iran’s aggressive policy, which destabilizes the region, must be curbed. He renewed his thanks to the Kingdom for joining the International Alliance for the Safety and Protection of Maritime Navigation and its role in contributing to the security of navigation and global trade.

The Saudi Press Agency (SPA) said Esper told MBS the United States will do “what is necessary to help Saudi Arabia defend itself,” as Gulf News put it:

During the call with Esper, the Saudi crown prince described the attack as a “dangerous escalation against whole world” and urged a “firm” stance to safeguard international peace and security, according to the agency. SPA also quoted Esper as stressing the need to curb Iran’s “hostile and destabilizing” policy in the region.

Military.com noted on Tuesday that U.S. officials have indicated Prince Sultan Air Base in the central Saudi desert is the most likely deployment option for American troops. U.S. Air Force personnel were sent to the Prince Sultan base on “short notice” last week to prepare it for operations after “tensions with Iran got a little heightened,” as Air Force Col. David Jackson explained.

Prince Sultan Air Base was used by American troops during Operation Desert Shield, the U.S. response to Saddam Hussein’s invasion of Kuwait in 1990, and was shuttered in 2003 during the Iraq War because U.S. operations were shifted to an air base in Qatar.

A senior U.S. official said on Tuesday that the Pentagon wants to “wait and see what other countries are going to do in supporting Saudi [Arabia]” before making final decisions. In particular, Defense Secretary Esper has spoken with the defense ministers of Britain, France, and Germany about countering the Iranian threat.

The exact number of U.S. troops heading for Saudi Arabia has not been finalized, in part because the Pentagon is awaiting commitments from European powers. The United Kingdom was quickest to indicate a willingness to participate in joint operations to protect Saudi Arabia.

“If we are asked, either by the Saudis or by the Americans, to have a role, then we will consider in what way we could be useful,” British Prime Minister Boris Johnson said on Monday.

Saudi Foreign minister Adel al-Jubeir said on Tuesday that a strong response to Iranian aggression is in the works and the United States will be part of it.

“We want to mobilize international support, and we want to look at a whole list of options – diplomatic options, economic options and military options – and then make the decision. This action will have consequences and Iran must know this,” Jubeir said from the sidelines of the U.N. General Assembly in New York City.

“When push comes to shove, there comes a point when even America’s patience runs out – and Iran must be aware of that,” he said.