EU and NATO leaders reacted with revulsion Tuesday to the twin bomb blasts at the Boston Marathon that killed at least three people.

"I condemn the appalling acts carried out in Boston and deeply regret the tragic outcome and loss of innocent lives. Those responsible for the atrocious acts will be brought to justice," said European Union President Herman Van Rompuy in a statement.

The attacks also wounded more than 100 and while President Barack Obama went on national television to guard against "jumping to conclusions," a senior White House official, speaking on condition of anonymity, said such an attack was "clearly an act of terror."

EU foreign affairs head Catherine Ashton said the attacks, "deliberately targeting men, women and children," were "reprehensible" and added: "We stand with the United States government and people in condemning this bombing."

European Parliament head Martin Schulz said "terrorism is never justified. We are with our American friends."

Meanwhile, NATO Secretary General Anders Fogh Rasmussen was also "deeply shocked."

"I express my heartfelt condolences to the families and loved ones of those who were killed, and I wish a full recovery to those who were injured. My thoughts are with the people of Boston and all of the United States."