The national police were following several leads Monday, following an explosion near the Vietnamese Friendship Monument in Phnom Penh Sunday morning, a spokesman said.
The explosion came from one of three homemade bombs planted in barrels near the monument, which stands in a grassy park near the National Assembly complex.
The two remaining bombs had to be diffused by experts from the Cambodian Mine Action Committee later Sunday. Officials said they contained TNT powder and fertilizer.
No one was injured in the blast, and nothing was damaged.
"We have a lead," Interior Ministry spokesman Khieu Sopheak said Monday. He declined to give the names of suspects. "We only have a light for the lead to the suspect's arrest. When we arrest the suspect, we will ask him, and he will tell us who is behind it."
A human rights worker said Monday he was concerned the explosion could increase the security pressures on members of the Khmer Kampuchea Krom, who have been protesting in recent weeks following the disappearance of monk Tim Sakhorn. Tim Sakhorn was defrocked in June for allegedly stirring unrest against Vietnam. He has not been seen since, and rights groups fear he was forcibly sent to Vietnam.
"I am concerned about yesterday's explosion, said Ou Vireak, director of the Cambodian Center for Human Rights. "I am concerned especially because it puts pressure on a number of people protesting the lack of freedom of the Khmer Kampuchea Krom."
Phnom Penh police commissioner Touch Naroth declined comment Monday, but told reporters on Sunday after the blast he would seek clear evidence before commenting.