An explosion inside the zoo in Sri Lanka's capital Colombo wounded four people on Sunday, a military spokesman said.
The cause of the blast was not known, Brigadier Udaya Nanayakkara said. "Investigations are going on and no further details available."
The blast came a day after a bomb blamed on Tamil Tiger rebels killed 18 people and injured more than 50 civilians in the town of Dambulla in central Sri Lanka.
"There has been an explosion. I heard a loud noise inside the zoo," an official said from the facility in the Dehiwala suburb of Colombo.
The Liberation Tigers of Tamil Eelam, fighting for a separate homeland for minority Tamils in the north and east of the island, are frequently blamed for suicide and bomb attacks in the capital and elsewhere.
Fighting between the Sri Lankan military and the LTTE fighters has escalated after a six-year ceasefire expired last month.