The device was found in a residential complex in the Cibubur area, and exploded soon after a police bomb squad removed it to an empty plot of land. It followed a series of "book bombs" blamed on an Islamist group.

"As the police bomb squad detected that the package contained explosive materials, they took it away. Soon after that it exploded," national police spokesman Boy Rafli Amar told reporters.

Local police chief Dadang Raharja told Metro TV: "The package was inside a plastic bag and on it a warning was written that it contained a bomb with some Arabic writing."

Jakarta police have found four "book bombs" since Tuesday. One, sent to Ulil Abshar Abdalla, a well-known liberal Muslim figure who espouses pluralism and religious tolerance, exploded and injured four people.

Another, also sent in a hollowed-out book, was discovered Thursday at the Jakarta home of musician Ahmad Dhani, who is known for his songs protesting against religious extremism.

The others were mailed to former top counter-terrorism police official Goris Mere and Yapto Suryosumarno, chairman of youth organisation Pemuda Pancasila.

City police chief Sutarman told the Detikcom news website on Friday, "I've ordered a deployment of one bomb squad unit in every police station here in Jakarta."

Jakarta police earlier said they expected more bombs to be distributed in the capital, calling on people to report any suspicious package immediately.

President Susilo Bambang Yudhoyono said Thursday he had instructed the National Intelligence Agency, police and the military to investigate the bombs and not "give anyone the opportunity to rip apart the security situation".

The Muslim-majority country of 240 million people has been rocked by a series of bombings staged by regional terror network Jemaah Islamiyah in recent years, including the 2002 Bali bombings which killed 202 people.

National Anti-Terror Agency (BNPT) chief Ansyaad Mbai told AFP Wednesday that he believed the same group was behind the "book bombs".