Thai officials: Bangkok bomb 'unlikely' work of foreign group

In a televised statement Thursday, however, military spokesman Col. Winthai Suvaree cast doubt on an international connection.

"Security agencies have collaborated with intelligence agencies from allied countries and have come to the same preliminary conclusion that the incident is unlikely to be linked to international terrorism," Winthai said.

When contacted by telephone for clarification, he said that a link to global terrorism hadn't been ruled out. "We still have to investigate in more detail," he said.

Winthai also said on television that Chinese tourists, who were among the victims, were not the "direct target."

The Monday evening attack at the Erawan Shrine, a popular tourist site that is known to attract Chinese visitors, left 20 people dead and more than 120 injured. Four Chinese citizens were among the dead.

No one has claimed responsibility for the blast, sparking a variety of theories into who might be behind it. One is that the blast was a revenge attack related to Thailand's recent deportation to China of more than 100 Uighur Muslims, or that it could have been carried out by foreign insurgent groups expanding their reach in Southeast Asia.

Other speculation points closer to home. Muslim separatists have been waging a low-level but deadly insurgency in southern Thailand since 2004, leaving more than 5,000 people dead. But virtually all their attacks have been confined to the southernmost provinces. Though there has been little violence aimed at Thailand's coup, whose leaders have cracked down on dissent, the "Red Shirt" movement that supported the ousted elected government clashed with the military in 2010 protests that left about 90 people dead. There could even be infighting within the army ahead of an annual military reshuffle.

The attack has raised concerns about safety in a city that draws millions of tourists, but life has returned to normal quickly. Subways and shopping malls were bustling and aside from bag inspections at stores and hotel entrances, there was little visible extra security. Authorities say security has been tightened citywide mainly with plain clothed officers.

Police officials told reporters Thursday that authorities believed those behind the blast must have planned it in advance, maybe a month ahead of time, and would have needed a site inspection team, bomb makers, bombers and an escape team.

"This was a network. We think they would have needed at least 10 people," said national police spokesman Lt. Gen. Prawut Thavornsiri.

The comments appeared to be speculative, not based on firm evidence. National police chief Somyot Poompanmoung said later Thursday, "I didn't say there are 10 suspects. I said theoretically they need more than 10 people."