Obama: Boston, US 'undaunted'

President Obama declared Boston and the nation remain "undaunted" during a memorial service Thursday for the victims of the Boston Marathon bombings.

"We may be momentarily knocked off our feet. But we'll pick ourselves up. We'll keep going. We'll finish the race," Obama said.

In a speech that was equal parts tribute to Boston and memorial to the victims of Monday's attack, Obama praised the city for its resilience and determination in the face of terror.

"I have no doubt: you will run again. You will run again 'cause that's what the people of Boston are made of. Your resolve is the greatest rebuke to whoever committed this heinous act," Obama said. "If they sought to intimidate us, to terrorize us … it should be pretty clear right now they picked the wrong city to do it."

Obama also vowed to perpetrators of the bombing that they would be found and brought to justice.

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

Obama spoke at the Cathedral of the Holy Cross, just a mile from where investigators continued to comb through evidence from the blast that killed three people and injured 170 others huddled near the finish line. He said that the "small, stunted individuals" responsible for the attack would only strengthen the country's resolve.

"A bomb can't beat us. That's why we don't hunker down. That's why we don't cower in fear. We carry on. We race. We strive. We build and we work and we love."

He also pledged that the world would gather again next year in Boston for the marathon, the central event of the state's Patriots' Day holiday.

"The world will return to this great city to run harder than ever, to cheer louder than ever," Obama said.

The president spoke to a nation still reeling from the terrorist attack, with fears deepened by authorities admitting they had little indication who was responsible for the bombing. At a hearing on Capitol Hill, Homeland Security Secretary Janet Napolitano said the FBI wanted to speak with two men seen in at least one video from the marathon, but stopped short of classifying them as suspects.

Deputy press secretary Josh Earnest said Obama had been briefed on the status of the investigation before leaving the White House on Thursday morning. But Earnest was cagey when asked about updates on the search for suspects in the attacks, deferring questions to the FBI.

While in Boston, the president plans to meet with law enforcement officials, first responders and some of those injured in the bombing.

Obama traveled to Boston with Vicki Kennedy, the widow of the late Sen. Ted Kennedy (D-Mass.), and members of the Massachusetts congressional delegation, including Democratic Sens. Elizabeth Warren and Mo Cowan. He was greeted at the airport by Gov. Deval Patrick and Ed Davis, the Boston police commissioner.

Patrick, who spoke before Obama, said the tragedy had "exposed the best of who we are."

"We will recover and repair. We will grieve our loses and heal. We will rise and we will endure," Patrick said.

Current and former Massachusetts lawmakers were in attendance, including former Republican presidential candidate Mitt Romney and former Democratic presidential candidate Michael Dukakis.