Indonesia's defence minister has named an Islamic militant group as the prime suspect in the attack on a luxury US-run hotel in Jakarta.
Ten people were killed and scores injured in the hotel blast
Matori Abdul Djalil said he was "sure" Jemaah Islamiah (JI) was behind the bombing of the Marriott Hotel, in which 10 people died.
He also linked JI with al-Qaeda, saying that members had trained with the group in Afghanistan and Pakistan.
The US has warned that militants may be planning more terror attacks against its interests in Indonesia.
"As security is increased at official US facilities, terrorists will seek softer targets," the State Department said in a travel advisory.
"These may include facilities where Americans and Westerners are known to live, congregate, shop or visit."
Americans were among the scores injured in Tuesday's blast.
Indonesian police have identified the severed head of the presumed suicide bomber of the Marriott hotel as that of a JI member.
However, Mr Djalil was the first senior official to say he believed the attack was the work of JI - already blamed for last year's Bali bomb attacks which killed more than 200 people.
"I affirm that this group is behind the Marriott bombing, based
on intelligence reports following the arrest [in July] of nine
suspects who are also JI members," the defence minister said.
Asked for comment on JI's size, he said it had many members in Indonesia but was "not massive".
Members had bomb-making or other "special abilities", he added, honed in such places as Afghanistan and Pakistan.
Pakistan's foreign ministry did not dispute that JI members may have been trained by al-Qaeda on its territory but it asked why Jakarta had not contacted it earlier.
"If the Indonesian Government had a lead on the training of the terrorists, they should share it with us so that we could further intensify our action," the statement said.
Afghanistan's foreign ministry said it was no surprise that suspects may have received training before the Taleban were overthrown.
"We all know that hundreds, if not thousands, of terrorists
used Afghanistan as a training ground," spokesman Omar Samad said.
"And certainly some of those people are scattered around the world today."
Indonesian investigators are exploring possible links between the Jakarta and Bali attacks.
In both cases, explosives were detonated by mobile phone and both bombs contained TNT mixed with a black powder, identified as potassium chlorate in the Bali case.
At least 33 suspected JI members are either on trial, or awaiting trial, for the Bali attacks.
Jemaah Islamiah was formed in the mid-1980s by two Indonesian clerics.
Its principal goal is the establishment of a unified South East Asian Islamic state stretching from southern Thailand, through the Malay Peninsula, including Singapore and across the Indonesian archipelago, and into the southern Philippines.