WASHINGTON, D.C. — Six days of fear over full-scale war with Iran broke into relief on Wednesday as President Donald Trump said he would refrain from hitting back over Tehran’s strikes on military bases housing U.S. troops in Iraq.

His decision to step back from an escalating confrontation with Tehran that began with the killing of an American contractor, and resulted in Trump’s targeted killing of Iran’s top general, has hit pause on a conflict that Washington feared was quickly spiraling out of control.

“The American people should be extremely grateful and happy,” Trump said, flanked by military officials and senior Cabinet members. “Iran appears to be standing down, which is a good thing for all parties concerned and a very good thing for the world.”

Iran retaliated against the Jan. 3 killing of Qassem Soleimani, the head of Iran’s elite Quds Force, by striking at two of America’s largest bases in Iraq on Tuesday night. The strikes did not result in any American casualties — a move that avoided Trump’s vow to retaliate in the event of any further bloodshed.

“We suffered no casualties. All of our soldiers are safe,” Trump said, crediting an early-warning system that “worked very well.”

Yet both sides continue to issue threats. While Iran’s foreign minister, Javad Zarif, said that his government’s operation to avenge Soleimani had concluded, U.S. forces remain on high alert in anticipation of additional attacks launched by Iran’s proxy forces throughout the Middle East.

Tehran has threatened to strike at any nation in the region from which any future American strikes are launched on Iran itself. Officials in Israel and the United Arab Emirates have said they are prepared to defend their cities, including the bustling ports of Haifa and Dubai, from any attack.

The day after Soleimani’s death, Iranian officials said they would abandon all limits on their enrichment of uranium — the fissile material that can be used to build nuclear weapons — set by Tehran’s 2015 nuclear agreement with world powers. Over the course of two decades, consecutive U.S. administrations have threatened military action in response to Iran’s expansion of its enrichment program.

Acknowledging that development, Trump opened his remarks on Wednesday by issuing a warning over Iran’s nuclear work.

“As long as I’m president of the United States, Iran will never be allowed to have a nuclear weapon,” Trump said, for the first time calling on China, Russia and European powers to fully abandon the 2015 agreement.

The president promised “powerful” new economic sanctions on Iran following the standoff, and said he was requesting NATO increase its supportive role alongside the United States in the Middle East.

“Today I am going to ask NATO to become much more involved in the Middle East process,” said Trump, flanked by Chairman of the Joint Chiefs of Staff Army Gen. Mark Milley and several other top military service chiefs.

He also suggested a willingness to open direct negotiations with Tehran over common interests, such as the fight against Islamic State.

But he said that military force remained an option going forward, either if Iran continues expanding its nuclear program or its “malign behavior” across the region.

“U.S. armed forces are stronger than ever before,” Trump said. “Our missiles are big, powerful, accurate, lethal and fast. Under construction are many hypersonic missiles. The fact that we have this great military and equipment, however, does not mean that we have to use it,” he said.

“We do not want to use it,” Trump said. “American strength, both military and economic, is the best deterrent.”

As Iran’s strikes were underway, Trump’s top national security advisers, including Defense Secretary Mark Esper and Secretary of State Mike Pompeo, went to the White House to brief the president. They visited again on Wednesday morning to offer Trump a detailed damage assessment.

Trump administration officials believe the nature of Iran’s retaliatory attacks were intended to send a message of strength at home — the strike utilized Iran’s ballistic missiles — while offering Trump with an off-ramp from direct conflict.

Senior Republican lawmakers were briefed by Trump on Tuesday night on the outlines of his remarks. Esper is scheduled to brief members of Congress on the situation later Wednesday.