The Trump administration is sending an aircraft carrier and a bomber task force to the Middle East - in a show of force aimed at Iran.
"In response to a number of troubling and escalatory indications and warnings, the United States is deploying the USS Abraham Lincoln Carrier Strike Group and a bomber task force to the U.S. Central Command region to send a clear and unmistakable message to the Iranian regime that any attack on United States interests or on those of our allies will be met with unrelenting force," White House national security advisor John Bolton.
"The United States is not seeking war with the Iranian regime, but we are fully prepared to respond to any attack, whether by proxy, the Islamic Revolutionary Guard Corps, or regular Iranian forces."
The statement did not identify what actions Iran may have taken that would prompt the United States to increase its military presence in the region.
The move is likely to intensify tensions with Iran, which the Trump administration blames for fueling instability across the Middle East.
It is the latest in a series of steps, including withdrawal from President Barack Obama's nuclear deal and designating the Islamic Revolutionary Guard Corps as a terrorist group, that signal the administration's desire to take a more confrontational approach toward Iran.
The Islamic Revolutionary Guard Corps designation had stoked fears that Iran might retaliate against US personnel or interests in the region, possibly via one of an array of armed proxy groups that include Lebanese Hezbollah and Shiite militias in Iraq.
Thousands of U.S. service members are stationed at large bases in Bahrain, Qatar and other locations in the area, while troops in Iraq and Syria continue to conduct operations targeting the Islamic State group.
The Nimitz-class Lincoln left the port of Norfolk, Virginia, earlier this spring.
The US is deploying the USS Abraham Lincoln Carrier Strike Group and a bomber task force to the US Central Command.
A carrier strike group can involve thousands of military personnel and include an aircraft carrier, cruisers, destroyer squadrons and frigate.
The US flexing its muscles follows Iran's religious leaders moving to expand their influence over the Shiite Muslim establishment in neighboring Iraq - in a gamble aimed at gaining sway over Iraq's largest religious group.
The Iranian campaign is most apparent in the holy city of Najaf, home to Iraq's clerical hierarchy and a gateway to the wider Shiite population, which represents about two-thirds of Iraqis.
In Najaf's dusty warrens, Iran has bankrolled schools and charities, built elaborate mosques and nurtured links with religious scholars in a bid to undermine the local clergy, who have long been fiercely independent.
Clerics tied to Iran are promoting its particular brand of state-sponsored Shiite theology in the city's seminaries and have been maneuvering to install one of their own as Iraq's "marja," or supreme religious authority, Iraqi political operatives say.
Posters of Sheikh Mahmoud Hashemi Shahroudi, a senior Iranian politician whom Tehran had backed for that powerful post before he died, are still plastered on Najaf's walls.
"Iran wants to abduct Najaf and make it its own," said Ghalib al-Shahbandar, an Iraqi analyst and former Islamist politician.
"It wants its own marja in Iraq and to control his movements."
But the Iranian theocracy's advances in Najaf have run into resistance, irking this city's turbaned luminaries, and could ultimately fuel resentment among Iraq's Shiites. Many Iraqis are already fed up with what they see as outsize Iranian interference in Iraq.
Iran's initiative to expand its religious influence complements its increasing efforts to project political, military and economic power in Iraq, where Washington and Tehran are competing for clout.
Iran has become particularly powerful after Tehran-backed militias took a leading role in vanquishing the Islamic State group, which had occupied a broad swath of northern Iraq, and Iranian proxy forces retain control over extensive Iraqi territory.
Allies of Iran, including former militiamen, have an influential role in Iraq's parliament. Iranian officials routinely mediate disputes among political and military factions.
Many local media outlets depend on Iranian largesse. Iranian imports - as varied as cosmetics, eggs and steel - are flooding local markets. And Iranian energy supplies help keep the lights on in Iraqi cities.