BOSTON - President Obama on Thursday celebrated this city's resilience in the face of a bomb attack that upended the legendary Boston Marathon, pledging that runners will return to the streets of an unbowed city next year.

"We may be momentarily knocked off our feet, but we'll pick ourselves up," Obama said at the close of an interfaith service aimed at bringing some healing to a city still reeling from the explosions Monday that tore apart runners and spectators at the finish line less than a mile from where he spoke. Three people were killed, nearly 200 wounded. "We'll keep going," he said. "We will finish the race."

His remarks at Boston's Cathedral of the Holy Cross came in a week of jarring news that included the attack in Boston, the threat of poisonous mail sent to Congress and the White House, and a devastating fertilizer-plant explosion in Texas.

Obama noted that he'd gone to school "across the river" - at Harvard Law School - and that he and first lady Michelle Obama, who also attended Harvard, had walked its streets.

"Boston may be your hometown, but we claim it, too," Obama said.

"This time next year, the world will return to this great American city to run harder than ever, and to cheer even louder for the 118th Boston Marathon," Obama said to a standing ovation.

He promised the perpetrators of the attack, whom he called "small, stunted individuals," that they'd be held accountable.

"Yes, we will find you, and yes, you will face justice," the president said. "But more than that, our fidelity to our way of life - to our free and open society - will only grow stronger."

Obama offered personal tributes to the three people who died in the explosions, and he and the first lady met before the service with the family of Krystle Campbell, 29. They later visited two of the hospitals treating the injured, meeting with the wounded, their families and some of the nurses and physicians caring for them.

The president also shook hands and offered hugs to first responders and marathon volunteers who crowded into Cathedral High School near the prayer service. Many had run toward the explosion to help the wounded, and Obama said at the service that they'd shown "that in face of evil, Americans will lift up what's good."

Several attendees at the service wore blue and yellow Boston Marathon jackets or had pinned blue and yellow ribbons to their shirts.

Many, fittingly, wore running shoes.