Twin hotel bombings on Friday appear to show the resilience of al-Qaida-linked militants in Indonesia despite a crackdown that many assumed had left them seriously weakened.
The blasts in the heart of the capital were the first in Indonesia in four years. They came 10 days after the re-election of a U.S.-friendly president in the world's most populous Muslim-majority nation.
The vote furthered the country's reputation as a beacon of secular democracy in the Islamic world. Suspicion has already fallen on the Jemaah Islamiyah terror network and its allies - especially Noordin Top, a Malaysian engineer who claimed responsibility for the last attack in Indonesia in 2005 and threatened more in a video tape.
Jemaah Islamiyah militants have been implicated in attacks since 2000, but the group rose to prominence after the 2002 nightclub bombings in the beach resort of Bali that killed 202 people, most of them foreigners.
One of the hotels hit on Friday, the J.W. Marriott Hotel, was also blown up by the group in a 2003 car bombing. The coordinated nature of the attacks - two blasts in the space of several minutes - is also a trademark of the network.
At its peak, Jemaah Islamiyah was believed to have a network of several hundred members across Malaysia, Indonesia, Philippines, Thailand and Australia. They received military training and were motivated by a desire to establish an Islamic state in the region.
The most dangerous members were the more than 60 Indonesians and Malaysians who traveled to Afghanistan in the late 1980s and early 1990s to fight the Soviet army or attend al-Qaida training camps. They returned to the region committed to al-Qaida style attacks on civilian Western targets. Arrested members testified in court that they were avenging Muslim deaths at the hands of American troops in Iraq and Afghanistan.
After Bali, militants staged an attack in Indonesia in each of the next three years: a 2003 car bombing outside the J.W. Marriott, a 2004 truck bombing outside the Australian Embassy, and triple suicide bombings on Bali restaurants by attackers carrying bombs in backpacks in 2005.
Police say some of the funds and direction for the first two attacks came from al-Qaida operatives that met Jemaah Islamiyah leaders in Bangkok, the Thai capital. Other funds are believed to have came from bank robberies.
They were also blamed for blasts in the Philippines and plotting attacks in Singapore.
The lull in attacks since 2005 was put down to a regional crackdown that began in earnest after the Bali attacks. The fact that the 2005 Bali attacks were smaller than the previous one and carried out on foot was taken as a sign the terrorists were being squeezed.
The United States and Australia, which lost 88 citizens in the first Bali attacks, provided funds and sophisticated surveillance equipment to Indonesia to help track down terrorists. Since 2002, more than 200 militants have been arrested, including several leaders and scores of foot soldiers. At least four have been executed, with the remainder being sentenced to terms between 3 years and life.
Malaysia and Singapore have also arrested alleged Jemaah Islamiyah members under laws that allow for indefinite detention without trial.
Most experts had predicted that the chances of another major attack were slim, but noted that several hardcore militants remained at large and appeared committed to terrorism.