BOSTON - US President Barack Obama vowed here on Thursday to find those behind Monday's Boston Marathon bombings and bring them to justice.

"We will find you ... You will face justice," said Obama while addressing a public interfaith service honoring the victims of the bombings, which left three people dead and over 170 injured.

Calling the bombings a "heinous act," Obama said that the bombers had clearly "picked the wrong city" in their attempt to " intimidate" and "terrorize" the American people.

The president said that people's prayers were with the families of those deceased and injured.

The blasts killed 8-year-old Martin Richard of Boston, 29-year-old Krystle Campbell of Medford, and Lu Lingzi, a Boston University graduate student from China.

Referring to Lu, Obama said: "She was a 23-year-old student far from home. And in the heartache of her family and friends on both sides of the great ocean, we are reminded of the humanity that we all share."

Obama also paid tribute to the city of Boston, which he called "one of the iconic cities" in the country.

"You will run again," Obama told those wounded in the bombings, who he said are beginning a "long journey of recovery" with the support of both the city and the nation.

Twin explosions occurred on Monday afternoon near the finish line of the Boston Marathon, causing heavy casualties. The authorities have called the blasts an "act of terror," but the motives and perpetrators remain unknown.

Obama signed a disaster declaration for the state of Massachusetts overnight, making additional federal resources available to state and local authorities.