WASHINGTON (AP) — Opening a new military front in the Middle East, President Barack Obama authorized U.S. airstrikes inside Syria for the first time Wednesday night, along with expanded strikes in Iraq as part of “a steady, relentless effort” to root out Islamic State extremists and their spreading reign of terror.

“We will hunt down terrorists who threaten our country, wherever they are,” Obama declared in a prime-time address to the nation from the White House. “This is a core principle of my presidency: If you threaten America, you will find no safe haven.”

Obama announced that he was dispatching nearly 500 more U.S. troops to Iraq to assist that country’s besieged security forces, bringing the total number of American forces sent there this summer to more than 1,500. He also urged Congress anew to authorize a program to train and arm Syrian rebels who are fighting both the Islamic State militants and Syrian President Bashar Assad.

Obama’s plans amounted to a striking shift for a president who rose to political prominence in part because of his early opposition to the Iraq war. While in office, he has steadfastly sought to wind down American military campaigns in the Middle East and avoid new wars — particularly in Syria, a country where the chaos of an intractable civil war has given the Islamic State space to thrive and move freely across the border with Iraq.

Speaking on the eve of the anniversary of the Sept. 11, 2001, attacks, Obama’s plans were also an admission that years of American-led war in the Middle East have not quelled the terror threat emanating from the region.

Obama insisted he was not returning U.S. combat troops to the Middle East. Even so, he acknowledged that “any time we take military action, there are risks involved, especially to the servicemen and women who carry out these missions.”

“But I want the American people to understand how this effort will be different from the wars in Iraq and Afghanistan. It will not involve American combat troops fighting on foreign soil,” he added.

The president’s announcements follow a summer of deliberation at the White House over how to respond to the violent Islamic State militants. While administration officials have said they are not aware of a credible threat of a potential attack by the militants in the U.S., they say the group poses risks to Americans and interests across the Middle East. Officials are also concerned about the prospect that Westerners, including Americans, who have joined the militant group could return to their home countries to launch attacks.

In recent weeks, the militants have released videos depicting the beheading of two American journalists in Syria. The violent images appear to have had an impact on a formerly war-weary public, with multiple polls in recent days showing that the majority of Americans support airstrikes in both Iraq and Syria.

The U.S. began launching limited airstrikes against Islamic State targets in Iraq earlier this summer at the request of that country’s former prime minister. But Obama vowed that he would not commit the U.S. to a deeper military campaign until Iraq formed a new government that allowed greater participation from all sects, a step Iraqi leaders took Tuesday.

Officials said Obama plans to proceed with both the broader airstrikes in Iraq and the strikes in Syria without seeking new authorization from Congress. Instead, he is to act under a use-of-force authorization Congress passed in the days after 9/11 to give President George W. Bush the ability to go after those who perpetrated the terror attacks. Obama has previously called for that authorization to be repealed, but he has also used it as support for strikes against terror targets in Yemen and Somalia.

Obama compared the new U.S. mission in Iraq and Syria to the actions in Yemen and Somalia, campaigns that have gone on for years.

“This counterterrorism campaign will be waged through a steady, relentless effort to take out ISIL wherever they exist, using our air power and our support for partner forces on the ground,” he said.

Obama is seeking authorization from Congress for a Pentagon-led effort to train and arm more moderate elements of the Syrian opposition. Even before his remarks, congressional leaders were grappling with whether to support that request and if so, how to get such a measure through the fractured legislature before the November elections.