Barack Obama, the US president, has arrived in Boston to attend a service for victims of the Boston Marathon bombing.
Monday's explosions tore through crowds watching the runners cross the Boston Marathon finish line, killing three and wounding 176 people.
Obama finds himself trying to heal emotional wounds barely four months after he offered solace to the families of 20 school children and six educators killed in a shooting in Newtown, Connecticut.
The president, accompanied by first lady Michelle Obama, was due to speak an interfaith service at the Cathedral of the Holy Cross.
Thomas M. Menino, the mayor of Boston, said: "I have never loved its people more than I do today," Menino said this morning. "We are one Boston. Nothing can tear down the resilience of this city."
Massachusetts Governor Deval Patrick was also scheduled to address the crowd.
Obama's trip to Boston comes a day after the Senate failed to muster enough votes to pass expanded background checks for firearms purchases. The president has been pushing for tighter gun controls in the wake of the Newtown shooting.
His message will be one of resolve, his spokesman Jay Carney said at the White House on Wednesday.
"It will be one of the commonality that we all feel as Americans with the people of Boston and those who were visiting Boston for the marathon, and who both endured this horrific event and then demonstrated their bravery in its immediate aftermath," Carney said.
Obama has vowed to find the person or people responsible for the blasts, which authorities say was likely produced by home-made bombs hidden in bags left amid the throngs watching the race.
Authorities in Boston were searching for a suspect seen on video taken before the two blasts struck. No arrests had been made, and the suspect in the video had not been identified by name, two US government officials said.