U.S. Defense Secretary Jim Mattis says the country is not immediately considering increasing troops in the Middle East in response to what he called Iran’s “misbehavior,” but warned that Washington and the world cannot ignore Iran’s actions.

In comments made at a news conference during a visit to Japan Saturday, Mattis called Iran the “biggest state sponsor of terrorism,” and said much of the rest of the world is watching.

Mattis: No Plans for More Troops in Middle East Over Iran Actions

He said, however, that despite the capability for the U.S. to send more forces to the Middle East, “right now, I don’t think it’s necessary.”

Mattis: No Plans for More Troops in Middle East Over Iran Actions

On Friday, the United States took its first steps in backing up tough talk about Iran, slapping new sanctions on 13 individuals and 12 entities linked to Tehran’s ballistic missile program and its proxies across the Middle East.

Mattis: No Plans for More Troops in Middle East Over Iran Actions

The targets include Iranian support networks in China and the United Arab Emirates that have been working to help Tehran obtain technology and materials needed to advance its ballistic missile program.

The Treasury Department said sanctions were also levied on individuals and networks working with Iran's Islamic Revolutionary Guard Corps' elite Quds Force and the Iranian-backed Lebanese terror group Hezbollah.

"These are just initial steps in response to Iranian provocative behavior," a senior administration official warned, calling Iran's recent behavior "not sustainable, not acceptable."

"Iran has a choice to make," the official added. "We will work positively with Iran when it abides by its international commitments while underscoring our commitment to aggressively counter Iran's destabilizing activities."

Friday's actions came as a result of what U.S. officials described as an ongoing process that included consultations with key U.S. agencies and also U.S. allies.

But officials said the trigger was Iran's January 29 test of a ballistic missile, which was "in defiance" of a U.N. resolution barring Iran from engaging in such tests.

A second senior administration official described Sunday's launch as "a clear threat to regional security."

The new sanctions are a culmination of the Trump administration's increasingly aggressive stance with Tehran, following a presidential campaign in which then-candidate Donald Trump said he was willing to rip up the nuclear deal former President Barack Obama and other world leaders negotiated with Iran.

Earlier this week, National Security Adviser Michael Flynn announced the U.S. was "officially putting Iran on notice."

Flynn was even more direct in a statement issued Friday. "The days of turning a blind eye to Iran's hostile and belligerent actions toward the United States and the world community are over," he warned.

White House Press Secretary Sean Spicer continued with the tough talk.

"President Trump is going to do everything he can to make sure Iran is stayed in check," Spicer said. "He is going to continue to be tough on Iran in a way that wasn't done in the past eight years."

Spicer also reiterated that the president was not taking any options off the table although "he understands the impact" of resorting to military action.

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Earlier Friday, Trump took to Twitter to warn Iran directly.

"Iran is playing with fire — they don't appreciate how 'kind' President Obama was to them, " Trump tweeted. "Not me!"

Iran is playing with fire - they don%27t appreciate how "kind" President Obama was to them. Not me!

Iranian Foreign Minister Mohammad Javad Zarif tweeted a response Friday.

"Iran unmoved by threats as we derive security from our people," Zarif tweeted. "We'll never initiate war, but we can only rely on our own means of defense."

Iran unmoved by threats as we derive security from our people. We%27ll never initiate war, but we can only rely on our own means of defense.

Late Friday, Iranian state television quoted a foreign ministry statement, which promised that Tehran would retaliate with sanctions of its own.

"Iran will impose legal restrictions on some American individuals and entities that were involved in helping and founding regional terrorist groups," the statement was quoted as saying.

The meaning or the impact of the promised Iranian sanctions was not immediately clear.

But senior administration officials in Washington said the new U.S. sanctions would have some bite.