An Indonesian man was seriously injured on Thursday when a nail bomb he was carrying on his bicycle exploded prematurely, police said.
A bomb in a bag the man was carrying while riding a bicycle blew up in the town of Bekasi, about 20 km east of Jakarta, police spokesman Boy Rafly Amar said.
"The explosion appeared to be of low intensity," Amar told Metro TV.
Amar said it was not clear if the man was intending to attack a target.
The bomb was crudely made from acetylene, gunpowder and nails, according to a police statement.
Police said a nearby police post might have been the target.
Local news websites ran a photo showing two pieces of paper carrying a message reportedly from the bomber saying: "This is retribution for you allies of Satan who have killed, executed and detained holy fighters."
Indonesian counter-terrorism police have arrested dozens of suspected Islamic militants and killed at least 15 others this year.
The world's most populous Muslim-majority country has been hit by a series of bomb attacks since 2000, notably the 2002 Bali bombings, in which 202 people were killed.
Three key players in the Bali bombings were executed by firing squad in 2008.