Washington (CNN) President Donald Trump is sending an additional 1,500 US troops to the Middle East as part of a "mostly protective" effort to deter Iranian threats, he said.

Many of the new forces will be engineers to support Patriot missile batteries and reconnaissance aircraft that are being newly deployed, a US official and a source familiar with the plan tells CNN.

CNN reported earlier on Friday that Trump has given his approval to acting Secretary of Defense Patrick Shanahan to deploy additional military resources to the Middle East to provide further deterrence against what the Pentagon believes is a rising Iranian threat against US troops in the region.

"We want to have protection," Trump said, speaking to reporters Friday at the White House. "The Middle East, we're going to be sending a relatively small number of troops - mostly protective. Some very talented people are going to the Middle East right now and we'll see what happens."

Asked how many troops, he said: "It'll be about 1,500 people."

"I don't think Iran wants to fight," Trump added, "and I certainly don't think they want to fight with us."

'They have actually attacked'

Shortly after Trump's remarks, the Pentagon announced that Iran's Revolutionary Guard Corps is responsible for attacks on four tankers at a port in the United Arab Emirates.

Vice Adm. Michael Gilday, director of the Joint Staff, told reporters at the Pentagon that "the Iranians have said publicly they were going to do things. We learned through intelligence reporting they have acted upon those threats and they have actually attacked."

The Trump administration has also notified lawmakers that it is using a pre-existing rule that allows it to bypass Congress in order to expedite arms sales to allies in the region.

The weapons sales, intended to push back on Iran's "malign activities," according to the administration, are worth $8.1 billion, Secretary of State Mike Pompeo said in a statement.

"These sales will support our allies, enhance Middle East stability, and help these nations to deter and defend themselves from the Islamic Republic of Iran," Pompeo said in a statement Friday.

The deployment and arms sales signal an intensified push against Tehran that is likely to raise concerns on Capitol Hill, where lawmakers have questioned the administration's threat assessment about Iran and have expressed concern that the US military build-up could lead to an accidental confrontation.

Deterrence

Shanahan and other administration officials have said the administration's focus is on deterrence and the protection of US forces in the region.

But senior military commanders already are talking privately about further troop level increases.

The deployment of the 1,500 did not give Gen. Kenneth F. McKenzie, the head of US Central Command, all of the forces he originally wanted to put into the region as a hedge against Iran, according to three US officials directly familiar with plans.

What was approved was essentially a package of emergency capabilities to deal with force protection.

Now a key question for the Pentagon is whether additional troops and capabilities will be sent, or whether there will be halt after this initial phase. "If additional assets or capabilities are needed to ensure" troop protection, Katie Wheelbarger, acting assistant secretary of defense for international security affairs, told reporters. "We will evaluate that at the time, based on the threat stream we see, but this is based on the specifics as we see it today."

'Only when necessary'

Shanahan acknowledged the dangers of some deployments in a Friday morning address at the US Naval Academy Commencement ceremony, saying "in my capacity, the most difficult decision is authorizing a mission that I know puts the men and women of our Armed forces in harm's way. I will continue to give those orders, but only when absolutely necessary."

The US has yet to publicly provide any evidence that shows increased Iranian threats.

The deployment announced Friday will include "approximately 1,500 US military personnel and consist of a Patriot battalion to defend against missile threats; additional intelligence, surveillance, and reconnaissance aircraft; an engineer element to provide force protection improvements throughout the region; and a fighter aircraft squadron to provide additional deterrence and depth to our aviation response options," Shanahan said.

Gilday said that about 600 of the 1,500 troops are part of a "Patriot battalion that's going to end up being extended, so the number of deploying personnel is really less than a thousand." The Pentagon later said that the number of boots on the ground will indeed increase by 1,500, explaining that the 600 members of the extended Patriot battalion will be joined by 900 new troops, as well as a Patriot unit that was originally intended to relieve the extended battalion as part of a normal rotation.

McKenzie, the commander of US Central Command, is putting a priority on sending defensive capabilities to the region, including the Patriots and intelligence gathering aircraft, according to the US official familiar with the deployment plans. That system is capable of shooting down ballistic and cruise missiles, as well as aircraft.

Additional deployments, if needed, could focus on more firepower, such as ships and aircraft, the official said.

CENTCOM oversees US military operations in the Middle East.

Drone surveillance

The US military also wants to send military engineers to the region to improve airfield security at bases CENTCOM would like to use. Another strategy will be to try to base some forces at locations out of the range of any potential Iranian missile attack. One such location might be Prince Sultan Air Base in Saudi Arabia according to some officials. It is not clear if an agreement with the Saudis has been reached.

The CENTCOM deployment request also includes both manned and unmanned aircraft for intelligence, surveillance and reconnaissance to monitor the movement of Iranian forces, including their increased readiness.

Pentagon officials have said that military intelligence assessments in the last several days underscored increased Iranian military readiness along their coastline and the thousands of short and medium range ballistic and cruise missiles in their inventory that could strike US targets in the region.

Those assessments have been questioned by lawmakers, who said after closed-door briefings Tuesday from Shanahan and Secretary of State Mike Pompeo that the threat level from Iran was not unusual. Sen. Chris Murphy, a Connecticut Democrat who sits on the foreign relations committee, said Monday that he was hearing "Republicans twist the Iran intel to make it sound like Iran is taking unprovoked, offensive measures against the US and our allies."

Murphy and other lawmakers argue that Iran's moves are "predictable" deterrence steps, given the US decision to send warships to the Gulf region a few weeks ago and the Trump administration's ongoing campaign to throttle Iran's economy with sanctions.

Adding to confusion about the nature of the threat Iran poses, Trump told reporters on Monday evening that "we have no indication that anything's happened or will happen, but if it does, it will be met obviously with great force."

Senators from both parties had also criticized the administration after hearing Thursday that the White House was planning to bypass Congress to sell new bombs to allies in the region, with some calling it an abuse of power and a dangerous precedent.

A section of the Arms Control Act allows the White House to waive a traditional 30-day congressional notification period for arms sales if the President declares an emergency, thereby preventing Congress from being able to put a hold on those arms deals.

If Iran wants to fight, that will be the official end of Iran. Never threaten the United States again! — Donald J. Trump (@realDonaldTrump) May 19, 2019

Republican Sens. Lindsey Graham of South Carolina and Rand Paul of Kentucky, anticipating the move Thursday, said they would oppose it. On Friday, Murphy said the move "sets an incredibly dangerous precedent that future presidents can use to sell weapons without a check from Congress."

Sen. Dianne Feinstein, the California Democrat who sits on the Senate Intelligence Committee, said that Trump's decision to sell arms outside the standard review process "is unacceptable."

In contrast to the doubts expressed by lawmakers and the President's characterization of the situation, the US military strongly believes the increased threat from Iran that emerged earlier this month has not diminished, according to several officials.

'Very high confidence'

On Friday, the Pentagon said Iran's Revolutionary Guard Corps was responsible for attacks on four ships in the United Arab Emirates on May 12.

Gilday, the director of the Joint Staff, said Friday that the IRGC is responsible for the damage to four tankers in the Emirati port of Fujairah and said that a recent rocket attack on the Green Zone in Iraq, where the US embassy is located, was carried out by Iranian proxies.

Gilday did not provide any evidence of Iran's role in the attacks, but cited intelligence. "I can't reveal the sources of that reporting except to say with very high confidence we tie the Iranians to those," Gilday said.

Administration officials have previously not been as definitive. Asked on May 21 if Iran was behind the tanker attacks, Pompeo said "we haven't formed a definitive conclusion," and added "it's quite possible."

This story has been updated to reflect the Pentagon's explanation of the troop deployment numbers and Vice Adm. Gilday's correct title, which was originally misidentified in a Pentagon release