Indonesian police pledged Sunday to find those responsible for a bomb blast that injured 11 at Jakarta's main airport, suggesting that separatists or a regional terror group could be behind the attack.

The early morning blast near a Kentucky Fried Chicken restaurant sent smoke billowing through the busy domestic terminal and hundreds of people running for safety. Police said they had interviewed at least 10 witnesses but made no arrests.

The blast came as Indonesia appeared to be patching up its battered image and reigning in the violence that has been a hallmark of the country since the fall of Suharto in 1998.

It arrested 32 suspects in the Oct. 12 Bali bombings, made peace with separatist in the province of Aceh and managed to contain protests during the Iraq war. Pointing to the improved security, the U.S. State Department announced Friday that it was allowing families of embassy staff to return to Jakarta.

It remains unclear what effect the blast will have on the country's image or its economy but authorities spent much of Sunday trying to reassure the public. They said had strengthened security around the Sukarno Hatta International Airport -- which remained open Sunday -- and were "chasing the perpetrators of the crime".

"This was meant to terrorize people," Lt. Gen. Erwin Mapasseng said. "If people are scared, then these people have achieved their goal. We're asking people not to panic and to remain calm."

Indonesian Security Minister Susilo Bambang Yudhoyono told the state news agency Antara that the blast may have been the work of the Free Aceh Movement, which has been fighting a 26-year secessionist war with the government.

The two sides signed a peace pact on Dec. 9 but violence in the oil- and gas-rich province at the northern tip of Sumatra has flared in recent weeks. The government on Thursday canceled talks scheduled for the weekend to address the problems.

"It is probable that the separatist group was involved in the terrorist acts," Yudhoyono said. "We must increase our alertness."

Zaini Abdullah, a rebel leader exiled in Sweden, denied the group was behind the attack.

"Where is the evidence?" Abdullah said. "I think they are trying to portray us as terrorists and trying to convince the world we are terrorists. But we aren't terrorists. We are freedom fighters."

Police said later that Jemaah Islamiyah -- an al-Qaida-linked Islamic militant group believed to be behind last year's Bali bombings -- could also have orchestrated the airport attack. "We believe there are three groups that could have done this, the Free Aceh Movement, those linked to the Bali bombings or Jemaah Islamiyah," National Police Chief Gen. Da'i Bachtiar said.

Indonesia is the world's most populous Muslim nation and is struggling to deal with a list of terrorist and secessionist movements that have taken advantage of the country's political instability and increased freedom.

Last October, Islamic radicals blew up two nightclubs on the tourist island of Bali, killing 202 people in the deadliest terrorist strike since the Sept. 11, 2001, attacks in the United States. Trials for the main suspects are expected to begin in May.

Sunday's blast -- the second bomb in a week -- happened four days after Abu Bakar Bashir -- the alleged spiritual leader of Jemaah Islamiyah -- went on trial for treason.

Bashir is accused of involvement in a series of 2000 Christmas Eve church bombings that killed 19 people. He has denied accusations that those blasts were intended to whip up violence between Muslims and Christians in a bid to destabilize Indonesia's secular government.

Western intelligence officials claim that Jemaah Islamiyah wants to set up a hardline Islamic state across Southeast Asia. Bashir, a Muslim cleric, has denied the charges and insists the group doesn't exist.

The airport blast also follows an announcement Wednesday that police raids resulted in the arrests of 18 suspected Jemaah Islamiyah members, including three wanted in the Bali bombings.

Bashir's hand-picked successor, Abu Rusdan, was among those arrested.

Sunday's blast occurred at about 6:30 a.m. near a Kentucky Fried Chicken restaurant, gift shop and cafe.

Mapasseng said the bomb appeared to be a small pipe bomb, noting that investigators had found shards of pipe, a battery and timer at the scene. He also said bomb appeared similar to one that exploded outside the main U.N. building in downtown Jakarta on Thursday and two last month in the northwestern city of Medan. No one was injured in the three blasts.

Mapasseng said police also found a bag near the blast site which may have contained the bomb, supporting witnesses who said they saw a bag outside the restaurant minutes before the explosion.

The bomb went off when the airport was relatively busy, with families and businessman catching flights to far-flung locations like Papua or Sulawesi.

Witnesses described a brief electrical power outage followed by a deafening explosion. Then panic, as smoke wafted through the terminal and crowds rushed for the exits, stepping over piles of broken glass and pools of blood.

"I was having a cigarette in front of the Kentucky Fried Chicken restaurant and then suddenly there was a big explosion," said Supryanto, a taxi driver. "There was smoke everywhere. I saw people running and two people on the ground passed out."

Three of the injured remained in local hospitals, including an 18-year-old girl who lost her left leg.

"As religious people, we have to believed this our destiny," said Milka, who was visiting her daughter Sylvia at the Tangerang Hospital. "We hope that such incidents like this will not happen again. We just hope. All we can do is surrender to God."