According to CNN, US forces and air-defense missile batteries across the Middle East were placed on high alert overnight Monday to possibly shoot down Iranian drones as intelligence mounted about a threat of an imminent attack against US targets, two US officials tell CNN.

As CNN reports, the alert reflects the heightened tensions between the US and Iran in the wake of last week’s US drone strike that killed a top Iranian general, Qasem Soleimani. US officials have claimed the strike against the general was carried out to prevent an “imminent” attack in the region that would have put American lives at risk, but have so far declined to provide details about the intelligence.

According to CNN, US intelligence also has observed Iran moving military equipment, including drones and ballistic missiles, over the last several days. US officials said the movement may be an Iranian effort to secure its weapons from a potential US strike, or put them in positions to launch their own attacks.

“There were indications that we needed to monitor the threats” even more closely than is already being done, one of the US officials said, referring to Monday night’s state of heightened alert. The second official described it as “all Patriot batteries and forces in the area on high alert” against an “imminent attack threat.”

Iran has put missiles on its drones that have been used in other attacks, including a significant attack on Saudi oil installations last year. While forces have already been on high alert for several days, they were even more vigilant Monday night, both officials said.

As CNN reports, Based on the intelligence, the US was watching for potential attacks specifically against US locations in Iraq, Kuwait, Saudi Arabia, the United Arab Emirates and Jordan.