At least nine people were killed in a series of bomb blasts at two hotels in the Indonesian capital Jakarta.
More than 50 people were injured in the attacks at the JW Marriott and the Ritz-Carlton hotels.
A car bomb also exploded along a toll road in north Jakarta, police said without giving further details. Indonesia's Metro TV said two people had been killed. An unexploded bomb was also later found at the Marriott.
The apparently co-ordinated bombings are the first in several years and follow a period in which the government had made progress in tackling security threats from militant Islamist groups, bringing a sense of political stability to southeast Asia's biggest economy.
Suspicion is likely to fall on remnants of the Jemaah Islamiyah group, blamed for previous attacks including a car bombing outside the Marriott in 2003 as well as bombings on the resort island of Bali the previous year that killed 202 people.
Witnesses said the bombings at the Marriott and the Ritz-Carlton were minutes apart. The hotels are near each other in a business area home to many offices, embassies and bars.
Hundreds of police, some soldiers and ambulances attended the scene. Scores of foreigners and Indonesian hotel guests milled outside, some still wearing bathrobes.
The windows in the first floor of the Ritz-Carlton were blown out, indicating the blast may have been in the restaurant, which would have been busy with breakfast at the time.
A visibly upset President Susilo Bambang Yudhoyono, re-elected this month on the back of improved security and a healthier economy, said the bombings were the act of a terrorist group bent on damaging the country.
Both the parliamentary elections in April and the presidential poll this month passed peacefully, underscoring the progress made by the world's most populous Muslim nation since the chaos and violence that surrounded the downfall of ex-autocrat Suharto in the late 1990s.
