Four people have been killed and 17 others injured in a bombing in the western Colombian city of Medellin.
It was not clear who was behind the blast, but authorities had earlier blamed Marxist rebels for three, smaller explosions yesterday in the day that injured two people in the southwestern city of Cali.
The bombings came a week before the 40th anniversary of the Revolutionary Armed Forces of Colombia (FARC), a 17,000-member guerrilla army. The four-decade-old conflict claims thousands of lives a year.
"There is a general alert in the city," the Medellin government's secretary, Mr Alonso Salazar, told reporters.
Images broadcast on television showed what appeared to be a bloodstained wall at the blast site, littered with debris and wet from rains. Late night news reported smaller blasts elsewhere in the city, causing no injuries, which could not be immediately confirmed.
