Boston marathon bombing

Key Points

• The FBI launched a "potential terrorist inquiry" after two bombs at the Boston Marathon
• The blasts left three people dead - including an eight-year-old boy - and more than 150 injured
• At least 17 people were critically wounded, officials say, and the injuries include several amputations
• President Barack Obama said the attack was "an act of terror" but added authorities do not yet know who carried it out
• All times EST (GMT -4)