A suspected smoke grenade explosion on Tuesday at Indonesia's National Monument park, near the presidential palace in central Jakarta, injured at least two military officials, the capital's top police official said.
President Joko Widodo was not at the palace at the time of the blast, a presidential spokesman said.
It was not immediately clear if the blast resulted from a sectarian attack, but Indonesia, the world's most populous Muslim-majority country, has suffered a resurgence in homegrown militancy in recent years.
The park explosion was suspected to have been caused by a smoke grenade, and two injured military officials had been taken to hospital, Jakarta's police chief, Gatot Eddy Pramono, told a televised news conference.
The two injured officers were doing exercises in the park at the time, Jakarta military chief Eko Margiyono added.
Asked if the blast was the result of an attack, Pramono responded, "We haven't concluded so, because we're still investigating."
Earlier, Jakarta police spokesman Argo Yuwono told Kompas TV
"There was a blast, but we're still checking what the source was." He added, "Injured victims have been taken to hospital," but did not elaborate.
Last month, six people were wounded after a 24-year-old university student blew himself up outside police headquarters in the Indonesian city of Medan.
The attack was linked to the Islamic State-inspired Jamaah Ansharut Daulah (JAD), responsible for a series of attacks across the country.
In October, a suspected Islamist stabbed and wounded former security minister Wiranto at a function to open a university building. Wiranto, who uses just one name, like many Indonesians, had to have surgery but has since left the hospital.