Foreign leaders and governments around the world are condemning the bombing at the Boston Marathon, which left at least three people dead and dozens others injured.
NATO Secretary General Anders Fogh Rasmussen expressed "deep shock" at the attack and offered condolences to those impacted. In a statement, he said his thoughts are with the people of Boston and all of the United States.
European Union President Herman Van Rompuy condemned what he called the "appalling attacks" and expressed confidence that the perpetrators will be brought to justice.
The Boston Marathon
2013 more than 23,000 runners
Last year, runners from 92 countries took part
Race passes through eight cities and towns
Held on Patriots' Day, a state holiday in Massachusetts
Only U.S. marathon that maintains qualifying times
World's oldest still-running annual marathon, first held in 1897
United Nations Secretary General Ban Ki-moon lamented the "senseless violence." He said the incident was even more appalling because it took place at an event known "for bringing people together from around the world in a spirit of sportsmanship and harmony."
Pakistan's Foreign Office condemned the "terrorist attacks" and said the government and people of Pakistan are "deeply shocked and saddened" by the "despicable act."
Related - China Reacts to Boston's Bombing
Deadly bombings in the United States
April 15, 2013: Twin blasts at the Boston Marathon kill at least 3, injure more than 140
September 11, 2001: Hijacked jets crash into World Trade Center, Pentagon and a Pennsylvania field killing nearly 3,000
July 27, 1996: Atlanta Summer Olympics bombing kills 2, injures more than 100
April 19, 1995: Car bomb at Oklahoma City federal building kills 168, injures more than 500
February 26, 1993: Van explosion in World Trade Center garage kills 6, injures more than 1,000
December 29, 1975: Bomb at New York's LaGuardia Airport kills 11, injures 75
September 16, 1920: Bombing in New York's Wall Street area kills 40, injures hundreds
Meanwhile, the Pakistani Taliban, which has in the past claimed responsibility for attempted attacks in the U.S., denied having any role in the Boston bombing.
Afghan President Hamid Karzai also denounced the attack "in the strongest possible terms." Offering condolences and sympathies to the families of the victims, Mr. Karzai said those in his country "feel better the pain and suffering arising from such incidents."
The Organization of Islamic Cooperation also strongly condemned what it called the "cowardly attacks." In a statement, the OIC said it has fought against terrorism in all its forms, and offered its condolences, prayers and support to the people of Boston.
In India, Prime Minister Manmohan Singh responded by expressing his "solidarity with the American people in the struggle against terrorism." In a message to President Barack Obama, Mr. Singh offered India's full support in investigating the attack.
Somali President Hassan Sheikh Mohamud spoke out against the attack on the innocent athletes and their supporters, calling the bombing "the most depraved and vicious act of cowardice."
Somali insurgent group Al-Shabab, meanwhile, mocked those injured and killed in the twin blasts. On its English-language Twitter page
, the Islamist group said the attack represents just a "tiny fraction" of the pain U.S. soldiers inflict on innocent Muslims around the world.
No one has yet claimed responsibility for the bombing.