WASHINGTON — President Donald Trump has ordered the deployment of about 1,500 additional U.S. troops to the Middle East amid rising tensions with Iran, according to two people familiar with the matter.

The purpose of the deployment is to enhance the protection of forces already in the region that are dedicated to missile defense, freedom of navigation in Persian Gulf waters and other objectives, according to a Pentagon notice to congressional defense committees obtained by Bloomberg. It wasn't immediately clear where the troops would be sent.

While people familiar with the decision called the deployment "initial," it falls far short of Trump's statement that in the event of hostilities with Iran he would be willing to send many times more than 120,000 troops suggested in a New York Times report last week. The president has repeatedly signaled in recent weeks that he is open to talks with Iran's leadership, though he's suggested officials in Tehran need to reach out to him first.

The troop decision follows comments by Acting Defense Secretary Patrick Shanahan on Thursday that the Pentagon was focused on having "the right force protection" in the region.

"Our job is deterrence. This is not about war," Shanahan told reporters. "We have a mission there in the Middle East: freedom of navigation, you know, counterterrorism in Syria and Iraq, you know, defeating al Qaeda in Yemen, and then the security of Israel and Jordan."

The president's decision comes after the Trump administration said that it had evidence Iran is threatening possible attacks on American interests or allies in the region. The administration earlier expedited the deployment of a carrier battle group to the Middle East along with a Patriot missile battery and additional bombers.

The additional troops will be engaged in activities including intelligence gathering, surveillance, reconnaissance, engineering and fire support, according to the Pentagon notice.

Iran has threatened to abandon the multi-nation nuclear deal of 2015 that remains in place despite Trump's withdrawal from the agreement a year ago. Iran is threatening to resume enriching uranium beyond levels permitted in the 2015 accord as a way to push France, Germany, the U.K. and the European Union to do something to relieve the effects of U.S. sanctions.

As the U.S. and Iran have each made moves in recent weeks, questions have been raised about the escalating threats. Sen. Angus King, a member of the Senate Intelligence and Armed Services Committee, asked on CNN this month, "Who's provoking who?"

"Are they reacting because they are concerned about what we're doing, or are we reacting because we're concerned what they're doing?" asked King, an independent who caucuses with Democrats. "And that raises my second concern, which is miscalculation."

The deployment was reported earlier by CNN.

Sen. Jack Reed, the top Democrat on the Armed Services Committee, warned on Thursday that there is "significant" potential for an overreaction by Iranian personnel or militia in Iraq, Syria and Afghanistan to the U.S.'s new military deployments.

"The dangers are extreme in terms of miscalculation," Reed said in an interview.

The Rhode Island senator declined to discuss the Pentagon threat briefing he's received on the Iran situation but said he was "absolutely" concerned about miscalculation by Iran in reacting to the U.S. moves.

Asked about the Trump administration's decision to accelerate the deployment of the USS Abraham Lincoln aircraft carrier battle group and other military hardware to the region, Reed said "if it's a deterrence I think that's appropriate because we don't want to see an outbreak of conflict there."

"We did not want to signal to the Iranians, erroneously, that we were not prepared," he said.