US officials say the Pentagon is sending about 1000 additional American troops to the Middle East.
Commanders are bolstering security for forces and allies in the region from what authorities claim is a growing threat from Iran.
Officials say the deployment includes security forces and troops for additional surveillance and intelligence gathering in the region.
The troops are part of a broader military package of options that were initially laid out to US leaders late last month, totalling as much as 10,000 forces, Patriot missile batteries, aircraft and ships.
The latest decision comes as US Secretary of State Mike Pompeo and other top officials are trying to convince leaders in Asia and Europe that Iran was behind alleged attacks on shipping along a Middle East oil route.
New photos were released by the Pentagon that officials said show that members of Tehran's Revolutionary Guard were responsible for attacks last week on two oil tankers.
The images, many taken from a Navy helicopter, show what the Pentagon said were Iranian forces removing an unexploded mine from the side of the Japanese-owned Kokuka Courageous oil tanker in the Gulf of Oman.
Officials last week said the move appeared to be an attempt to remove forensic evidence from the scene of the attack. But it's not clear if examination of the mine would have made it definitively clear that the device was planted by the IRGC.
Other photos show a large hole on the side of the Courageous, above the water line, that officials say appears to have been caused by another similar mine.
Iran has denied involvement in the tanker attacks and has accused America of promoting an "Iranophobic" campaign.
Tehran, however, has repeatedly threatened to close the vital Strait of Hormuz, through which 20 per cent of the world's oil flows.
Pompeo said he made a number of calls to international leaders, trying to convince them that keeping the Strait of Hormuz safe and open is a problem they all must deal with.
Relations between the US and Iran have deteriorated in recent months, as the Trump Administration restored crippling sanctions and designated the Revolutionary Guard as a foreign terrorist organisation.
That increased pressure preceded a string of attacks that the US has blamed on Iran.
The Trump Administration found itself in the awkward position today of demanding that Iran comply with a nuclear accord that the US President has derided as the worst deal in history.
Iran announced today it would break a limit on uranium stockpiles established by a 2015 agreement with world powers that was intended to restrict the Islamic Republic's nuclear program in exchange for an easing of international sanctions.
US President Donald Trump withdrew from the agreement, signed by his predecessor, and reinstated punishing economic sanctions, resulting in sharply rising tensions that deteriorated further with Iran's warning that it could soon start to enrich uranium to just a step away from weapons-grade levels.
That put the State Department in the position of defending the limits set by the 2015 deal that was so maligned by Trump and his national security team.
"We continue to call on the Iranian regime not to obtain a nuclear weapon, to abide by their commitments to the international community," State Department spokeswoman Morgan Ortagus told reporters.
Trump appeared to say the deal should not be violated in a tweet that said "Iran to defy Uranium Stockpile Limits."
Supporters of the deal, meanwhile, blamed the Trump administration for Iran's provocative announcements, saying they were entirely predictable given the renewed US pressure.
"While Iran's frustration with Trump's reckless and irresponsible pressure campaign is understandable, we strongly urge Iran to remain in compliance with the nuclear deal," the Arms Control Association said in a statement.
"It remains in Iran's interests to abide by the limits of the agreement and to fully cooperate with the International Atomic Energy Agency's more intrusive monitoring and verification."
The European Union said that it will consider Iran to be complying with its obligations under a global nuclear deal up until the point scientific evidence emerges that it has breached its commitments.