The Pentagon is sending around 1,000 additional American troops to the Middle East, as commanders try to bolster security for forces and allies in the region from what authorities say is a growing threat from Iran.
Officials said 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 many as 10,000 forces, Patriot missile batteries, aircraft and ships.
The US President claimed on Tuesday evening that his tactics were working.
He said: "They are a much different country today than they were two and a half years ago when I came into office."
"When President Obama signed that horrible deal, they were screaming death to America.
"I haven't been hearing that lately," he added.
The latest decision comes as Secretary of State Mike Pompeo and other top officials reach out to leaders in Asia and Europe to on shipping along a Middle East oil route, and just hours after Iran announced it was going to break the uranium stockpile limit set by a nuclear deal in the next 10 days.
Mr Pompeo said: "We are there to deter aggression, now President Trump does not want war and we will continue to communicate that message while doing all the things necessary to protect American interests in the region."
In announcing the new deployment, acting defence secretary Patrick Shanahan said the forces are "for defensive purposes to address air, naval, and ground-based threats in the Middle East."
"The United States does not seek conflict with Iran," Mr Shanahan said.
"The action today is being taken to ensure the safety and welfare of our military personnel working throughout the region and to protect our national interests."
He added the US will continue to adjust troop levels as needed.
The announcement by Iran’s nuclear agency marked yet another deadline set by Tehran.
President Hassan Rouhani has already warned Europe a new deal needs to be in place by July 7 or the Islamic Republic would increase its enrichment of uranium.
Atomic energy spokesperson Behrouz Kamalvandi suggested Iran’s enrichment could reach up to 20%, just a step away from weapons-grade levels.
It appears as if Iran has begun its own maximum pressure campaign on the world after facing one from President Trump’s administration that deeply cut into its sale of crude oil abroad and sent its economy into freefall after pulling out of the Iran nuclear deal and imposing sanctions on the Middle Eastern country.
Europe has so far been unable to offer Iran a way around the US sanctions.
“If this condition continues, there will be no deal” anymore, Mr Kamalvandi said.
He accused the Europeans of “killing time” as the clock runs down.
The Iranian announcement appeared timed to strike just as European foreign ministers met in Luxembourg.
Federica Mogherini, the European Union’s top diplomat, declined to specifically address the Iranian announcement.
“At the moment, as of today, Iran is still technically compliant and we strongly hope, encourage and expect that Iran continues to comply,” Ms Mogherini told journalists.
She insisted she would await the next report on the issue from the UN’s nuclear watchdog, the International Atomic Energy Agency (IAEA).
Under terms of the 2015 nuclear deal with world powers, Iran can keep a stockpile of no more than 300kg (660 pounds) of low-enriched uranium.
The nuclear deal limits Iran to enriching uranium only to 3.67%, enough for power plants and other peaceful purposes.
But after America pulled out of the nuclear accord and escalated sanctions, Mr Rouhani set a July 7 deadline for Europe to come up with better terms for the deal or Tehran would boost enrichment further.
So far, a European mechanism called INSTEX to protect trade with Iran has yet to take off.
The danger, nuclear non-proliferation experts warn, is that at 20% enrichment, only a fraction of atoms need to be removed to enrich up to weapons-grade levels of 90%.
Iran maintains its nuclear programme is for peaceful purposes, but the 2015 deal grew out of Western concerns about the programme.
Under the accord, Iran agreed to limit its uranium enrichment in exchange for the lifting of economic sanctions.
While Iran has denied being involved, it laid mines in the 1980s targeting oil tankers around the narrow mouth of the Persian Gulf through which a fifth of the world’s crude oil passes.
On Monday, the Pentagon released new photos which it claims show that Iran’s Revolutionary Guard was responsible for the attacks.
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 is not clear if examination of the mine would have made it definitively clear that the device was planted by the Revolutionary Guard.
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 a similar mine.
Iran has denied involvement in the tanker attacks and has accused America of promoting an “Iranophobic” campaign.
However, Tehran has repeatedly threatened to close the vital Strait of Hormuz, through which 20% of the world’s oil flows.