One of the deceased has been identified as Julie Huynh, a 23-year-old French national who had spent the past six months volunteering in the public school sector. The other two died were also women, ages 27 and 31.
Of the injured, one is in grave condition but is expected to survive, while the other eight are in less serious condition.
It's unclear who's responsible. An anti-terror investigation is being conducted by the Colombian prosecutor’s office.
The U.S. Embassy in Bogota offered condolences in a series of tweets, adding that it's standing by to "provide any support requested by the Colombian authorities."
ABC News' Joshua Hoyos contributed to this report.