Upon United States' killing of Qassem Soleimani, Iran's powerful military commander, the country has promised severe revenge.
These threats of confrontation have put on high alert across the Middle East through the bases, ports and other installations where US troops are based or pass through, reported Washington Post.
On Friday, the Pentagon announced that it was sending an additional 3,500 troops to the region, while troops in Italy were put on standby, according to defense officials.
The troop escalation came just days after President Trump ordered an additional 750 US soldiers to the Middle East and 3,000 more to be on alert for future deployment, after pro-Iranian forces stormed the US Embassy in Baghdad as part of a worsening cycle of violence.
The United States has tens of thousands of military personnel at bases and aboard ships across the Middle East, as well as arrangements with various countries to move soldiers and military equipment through airstrips and ports. Here's a look at some of these places, which could now be targets.
Iraq: Estimated 6,000 troops
US officials won't say exactly how many troops there are in Iraq or where they are based. There are an estimated 6,000 troops stationed across the country, including in the Green Zone, Baghdad's walled-off diplomatic area, and at al-Asad Air Base, where Vice President Pence visited US troops in November.
Tensions are extremely high in Iraq, which is stuck in the middle of the US-Iranian faceoff. That's put a spotlight on US citizens and installations there: On Friday, the State Department ordered all American citizens to leave the country.
Then, on Saturday, rockets were fired at the Green Zone and Balad air base, both of which have US troops stationed there. No one was hurt, and such attacks aren't uncommon. Still, it's left people bracing for more — and worse.
Syria: Estimated 800 troops
US officials are also tight-lipped about how many US troops are in Syria and where. As many as 800 remain in the country after the Trump administration abruptly withdrew soldiers in October. At that time, the number was around 2,000. The US garrison at Tanf, by the Syrian-Jordanian border, is now one potential flash point, the Brussels-based International Crisis Group has warned, because Iranian and Iranian-backed forces are deployed nearby.
Afghanistan: Estimated 14,000 troops
Afghanistan, where around 14,000 US military personnel are stationed and which is in southern Asia, could become another "arena for US-Iranian contestation," the ICG has warned. In November, Trump made a surprise visit to troops stationed at Afghanistan's Bagram air base.
Kuwait: About 13,000 troops
The United States has about 13,000 military personnel spread among several bases in Kuwait, according to the Congressional Research Service. The two countries have had a Defense Cooperation Agreement since the 1991 Persian Gulf War.
Jordan: About 3,000 troops
Jordan — bordering Iraq, Syria, Israel and the occupied Palestinian territories, as well as Saudi Arabia — is a strategically located US ally. Its Muwaffaq Salti Air Base was an important launching point in the battle against the Islamic State, and there are plans to upgrade the complex. In November 2016, three US soldiers were killed by a Jordanian air force sergeant in a rare shooting at King Faisal Air Base.
Saudi Arabia: Estimated 3,000 troops
In October, the United States announced that it was sending additional troops to Saudi Arabia as tensions with Iran continued to build. Saudi Arabia and Iran have long been regional rivals: The two are involved in a proxy war in Yemen. Washington has accused Iran of attacking oil and gas facilities in Saudi Arabia, which Iran has denied.
Bahrain: More than 7,000 troops
Bahrain hosts a US Navy base, where several thousand personnel are stationed or pass through. The island nation is a close ally of Saudi Arabia and has supported Trump's aggressive stance toward Iran. Bahrain also suppressed a Shiite uprising in 2011, putting it further at odds with Iran's government.
Oman: About 600 hundred troops
Oman hosts only a few hundred troops. In March, it signed a deal allowing US planes and warships to use some Omani airstrips and ports.
Most important, Oman is along the Arabian Peninsula near the Strait of Hormuz, the world's most important oil choke point. It's also where the United States and Iran for months have been engaged in oil tanker standoffs: Since withdrawing from the landmark 2015 Iran nuclear deal almost two years ago, the United States has increased pressure on Iran, including canceling waivers for countries to buy Iranian oil. Iran has in turn threatened to close access to the strait, which would severely constrain access to oil. Washington has also accused Iran of sabotaging oil tankers in the waterway, which Iran has denied.
United Arab Emirates: Up to 5,000 troops
The UAE is another country near the Strait of Hormuz that's been part of the tanker confrontations. It has hosted as many as 5,000 troops in recent years and is traditionally allied with Saudi Arabia and the United States. But rising tensions in the region have put the UAE on edge, and it has taken a somewhat more conciliatory approach to Iran in recent months.
Qatar: As many as 13,000 troops
Qatar is home to al-Udeid, the largest US military base in the Middle East. In 2018, Qatar announced a $1.8 billion plan to upgrade the base. The move came as Qatar was battling a blockade by rivals Saudi Arabia and the United Arab Emirates.
Turkey: Estimated 2,500 troops
Turkey hosts US troops at Incirlik Air Base, as well as other sites where NATO forces are deployed.