NUGEGODA, Sri Lanka — A bomb exploded Wednesday evening near the entrance to a popular department store in a busy Colombo suburb, killing 16 people and wounding more than 20 in a rare attack on civilians near the capital, the military said.

It added that the Tamil Tiger rebel group was responsible for the bombing.

The blast occurred just outside the four-story No Limits store in Nugegoda as commuters crowded a nearby bus stop during the evening rush hour, officials said.

Authorities did not immediately give a motive for the blast or speculate who was behind it. Earlier in the day, a female suicide bomber sent by the rebels killed one person and wounded two others in an unsuccessful attempt to assassinate a government minister in his office in Colombo.

The rebels' top leader blamed the government for a recent escalation of fighting in the more than two-decade-old civil war that has killed an estimated 70,000 in the Indian Ocean island nation.

The powerful blast at the department store shattered windows and sent piles of crumbled concrete onto the bloodstained sidewalk, according to an Associated Press photographer at the scene.

Crumpled and charred parts of motorcycles and three-wheeled taxis were scattered nearby.

Police and firefighters searched the debris for victims.

Military officials said at least 16 people were killed and 20 others wounded. At a nearby hospital, residents came in search of missing relatives. One girl who suffered a broken arm in the attack sat with her mother as she received treatment.

"I was on the top floor of a shoe shop with my wife and child when I heard a big blast and there were glass pieces all over us," resident A. Jayasena told AP Television News. "As we ran away, I saw the entrance of the No Limit shop burning, and in the midst of it, a schoolgirl on the floor trying to get up and then falling back again."

Jayasena and his daughter suffered minor injuries, while his wife was in the hospital being treated for more serious wounds, he said.

The bomb may have exploded when a security guard at the mall became suspicious about a parcel and tried to open it, a defense official said, speaking on condition of anonymity because he was not authorized to speak to the media.

The suicide bombing targeted the offices of Douglas Devananda, the minister of social services and the leader of the Eelam People's Democratic Party, an ethnic Tamil party considered a rival to the separatist Tamil Tigers, the military said.

Devananda, the target of repeated assassination attempts, was not injured in the attack, the military said. The blast killed one of his staff members and injured two others, one critically, said Dr. Hector Weerasinghe, the medical director of Colombo National Hospital. The bomber was also killed.

The rebel group has been fighting since 1983 to create a separate homeland for Sri Lanka's minority Tamils following decades of discrimination by governments controlled by the Sinhalese majority.