A suicide bomber blew himself up as police were praying Friday, wounding 28 people in the first attack on a mosque since extremists started targeting the predominantly Muslim country a decade ago.
The attack — which followed a nearly two-year lull in suicide bombings — occurred at a mosque inside a police compound in the West Java town of Cirebon. Local media reported that the bomber attended Friday prayers carrying a prayer rug and explosives hidden on his body.
Most of the people at the mosque were police officers, and the local chief of police was among the injured.
The victims were rushed to hospitals with nails, nuts and bolts embedded in their bodies, said Yeni Rahmawati, a hospital spokeswoman.
The bomber's identity has not yet been confirmed, and the remains were taken to a local hospital for investigation, NPR's Anthony Kuhn reported. A police spokesman labeled it a terrorist attack and said security would be heightened at police stations across the country.
Indonesia, a secular nation of 237 million, has been hit by a string of al-Qaida-linked attacks since the 2002 bombings on two crowded Bali nightclubs that left 202 people dead.
There have been three other major suicide bombings since then, the most recent targeting two luxury hotels in Jakarta in 2009, killing seven and wounding more than 50.
Many of the victims have been foreign tourists.
In the past year, however, militants seeking to carve out an Islamic state have said the country's moderate leaders and security forces would be their main targets.
They've attacked several police posts since then, but never a mosque, and their decision to do so during prayers Friday shows just how out of touch with public opinion they are. Houses of worship are commonly targeted by militants in Afghanistan, Pakistan and Iraq.
"It's really worrisome," said Mardigu Wawiek Prasantyo, an intelligence analyst, noting that the bombing during Friday prayers points to a "hardening of militants."
The mosque stood on the grounds of a police compound, but was open to the public.
West Java police chief Maj. Gen. Suparni Parto told El-Shinta radio that the mangled body of the suicide bomber was found at the scene.
The attacker was apparently wearing a suicide vest beneath his black robes and was sitting among dozens of worshippers when he set off the bomb, shouting "God is great!" said Agus Riyanto, a police spokesman.
Indonesia has battled Islamist militants with links to the Southeast Asian network Jemaah Islamiyah since the 2002 Bali bombings.
Though hundreds of suspected militants have been captured in a security crackdown in recent years, terrorists have proved resilient, with networks splintering and mutating.
NPR's Anthony Kuhn reported from Bangkok for this story, which contains material from The Associated Press.