Mohammad al-Chalabi, leader of a Jordan extremist Muslim Salafi group, has rejoiced over the tragedy in Boston, where two bombs exploded killing three and injuring over 140, many seriously.

The Bulgarian news agency BTA reports, citing AP, al-Chalabi has stated he was "happy to see the horror in America" and "American blood isn't more precious than Muslim blood."

The extremist leader has been sentenced to 7 year of jail for organizing attacks against western missions in Jordan in 2003. His organization is outlawed in the country.

A counterterrorism official based in Jordan has said the blasts carried the marks of an organized terrorist group like al-Qaida, but has not offered details and evidence.

Security measures for the US Embassy in Amman have been increased.

The death toll in the explosions has risen to three while more than 100 are reported injured, some seriously.

TV footage showed bloodied runners and spectators being treated at the scene and the road strewn with debris.

The FBI has said that they were looking at a "potential terrorist investigation," but it's not clear whether the origin was domestic or foreign. However, President, Barack Obama, has been more cautious in speaking of terrorism, stating in a TV address: "we will find out who did this" and that those responsible would feel the "full weight of justice."

Huge crowds, including thousands of foreign visitors, were in the area watching the runners take part in the world's oldest annual marathon.

It was also Patriots Day, commemorating the opening battle of the Revolutionary War.

The explosions occurred at about 2:45 p.m. Eastern Time, more than two hours after the first of the race's nearly 27 000 runners had crossed the finish line.

A photo by EPA/BGNES shows the road strewn with debris in the aftermath of two bomb explosions in downtown Boston, which occurred at the finish line of the city's very popular annual marathon.