President Trump on Thursday offered his “deepest condolences” to the families of four Americans killed in Syria in a suicide explosion claimed by the Islamic State, an attack that came less than a month after he declared the militants defeated and ordered 2,000 U.S. troops in the country to be withdrawn.

Trump offered his first public remarks on the deaths, which occurred Wednesday, during an address at the Pentagon on missile defense strategy.

“My deepest condolences to the families of the brave American heroes who laid down their lives yesterday in selfless service to our nation,” Trump said of the deceased, who included two soldiers, a Defense Department civilian and a military contractor. “These are great people, great, great people. We will never forget their noble and immortal sacrifice.”

Since Trump’s Dec. 19 announcement of the troop withdrawal, the administration’s strategy has been thrown into confusion, as Trump’s defense secretary resigned in protest. The announced pace of withdrawal has varied, and Secretary of State Mike Pompeo has sought aid from Arab allies. New conditions have been set for the U.S. departure, even as the president has said he is determined that the troops leave sooner rather than later.

Other powers have rushed to fill the coming void, including Turkey, Russia and the government of Iranian-backed Syrian President Bashar al-Assad.

Vice President Pence, who introduced Trump at the Pentagon event, made clear in his remarks that the administration remains committed to bringing the U.S. troops home.

President Trump gestures after signing H.R. 2, Agriculture Improvement Act of 2018, during a ceremony at the White House in Washington on Dec. 20, 2018. (Zach Gibson/Bloomberg)

“We will honor the memory of the fallen,” Pence said. “And their families and our Armed Forces should know, their sacrifice will only steel our resolve that as we begin to bring our troops home, we will do so in a way that ensures that the remnants of ISIS will never be able to reestablish their evil and murderous caliphate.”

In his remarks Thursday, Trump also pledged “a new era in our missile defense program” as he rolled out an initiative to expand the scope and sophistication of U.S. capabilities on a scale not seen since President Ronald Reagan’s “Star Wars.”

Known as the missile defense review, the document that Trump formally unveiled Thursday morning marks the first official update to U.S. missile-defense doctrine in nine years.

It comes as North Korea and Iran make advances in ballistic missile production, and as Russia and China press forward with sophisticated cruise missiles, short-range ballistic missiles and hypersonic glide vehicles that potentially threaten the security of U.S. forces and allies in Europe and Asia.

The Trump administration’s response is to call for urgent new investments in missile-defense technologies across the board, many of which the Pentagon pursued during the Cold War but abandoned after the collapse of the Soviet Union.

“Our goal is simple: to ensure that we can detect and destroy any missile launched against the United States anywhere, anytime, anyplace,” Trump said. “As we all know, the best way to keep America safe is to get America strong, and that’s what we’re doing.”

In the 1990s and 2000s, the Pentagon focused on building interceptors to down missiles launched from rogue states. Now it is again broadening its ambitions, both in terms of technology and missions. Whether the administration secures enough money to tackle such lofty ambitions in missile defense remains unclear.

In his remarks, Trump also touched on his ongoing impasse with Democrats in Congress over his demand for $5.7 billion in funding for a wall at the U.S.-Mexico border.

“We need strong barriers and walls,” Trump said. “Nothing else is going to work.”

He again blamed Democrats for the standoff, asserting that “the party has been hijacked by the open-borders fringe within the party.”

Karen DeYoung contributed to this report.