The US has warned citizens against travelling to Saudi Arabia, Bahrain, Iran, Iraq, Jordan, Lebanon, Kuwait, Oman, the UAE, Qatar, Syria, Yemen and Israel. All of the advisories referred to the threat of "terrorism".
Washington urged people to reconsider travel to Saudi Arabia owing to threats including the "risk of drone and missile targeting of American interests by Iran and the Iranian-supported Houthis", as well as armed conflict and terrorism. "Do not travel to the Yemen border due to terrorism," it added said in the advisory for the kingdom.
The US said the Houthi attacks on Saudi Arabia "have the potential to escalate rapidly beyond that immediate area".
A State Department official said after the announcement that the advisories were "not indicative of new capabilities from the Houthis, but reflect the strikes we have seen over recent days, including on the airport". That was a reference to attacks by the Iran-backed group on the Riyadh, Dammam, Najran and Jazan airports in recent weeks.
The deadly strikes caused disruption to air travel. Riyadh's King Khalid International Airport only partially reopened after it was closed this month and international services have not yet been fully restored.
The latest Houthi attack on King Fahd International Airport in Dammam, in the Eastern Province, killed two people and injured eight, Saudi Arabia's Civil Aviation Authority said on Wednesday.
Fears are growing of a renewed escalation between the US and Iran. On Friday, US President Donald Trump said Washington may carry out another military operation against Iran if a deal was not reached.
"We may do another little Epic Fury," Mr Trump told a rally in Florida yesterday, using the US military's term for its war on Iran. "If they're smart, they'll just say, 'Let's get down to business.' But, you know, I doubt they'll do that because perhaps they're not smart."
Earlier this month, he said the US would not strike Iran before the November 3 midterm elections.
Iranian officials have vowed to carry out an even more widespread response to any new attack than the strikes Tehran launched across the region after February 28. Cables, data centres and artificial intelligence sites could be attacked by Tehran, Iran's National Security Council chief Maj Gen Mohsen Rezaei told Iranian media this week.
The US continues to impose a naval blockade on Iran’s ports, while Tehran regularly attacks ships in the Strait of Hormuz.