UN Secretary-General Ban Ki-moon on Monday condemned the bombing at the Boston Marathon, calling it "senseless violence".

Speaking at a ceremony at UN Headquarters commemorating the 19th anniversary of the Rwanda genocide, Ban said the bombing "is all the more appalling for taking place at an event renowned for bringing people together from around the world in a spirit of sportsmanship and harmony".

He said that although reports on the incident were still coming in, it was already known that there are dead and wounded.

"For now I just wanted to say that my thoughts are with everyone in Boston," Ban said, expressing his deepest condolences to the families of the victims and wishing those wounded a speedy recovery.

Two explosions took place near the Boston Marathon finish line on Monday afternoon, killing at least three people and injuring over 100.