By Jill McGivering BBC Asia analyst

Prime Minister Thaksin Shinawatra has described the violence as the work of criminals.

He, along with senior officials, seemed keen to dismiss the theory it could be the work of Islamic separatist groups.

Hambali was arrested in Thailand last year

Now they sound less sure. The attacks were well organised and carefully co-ordinated.

Officials now acknowledge Islamic separatists may have been involved.

The authorities will want to quash speculation that the Islamic separatist movement in its Muslim-majority southern provinces could be resurfacing.

Apart from occasional attacks from a small group of radicals, violence has been largely contained since the late 1980s, partly the result of government efforts to improve integration and development.

But now, with the war on terror, there is renewed anxiety about Islamic movements in South East Asia - and the links between them.

Investigations into those convicted of involvement in the Bali bombings showed evidence of a tighter, more comprehensive regional network than previously suspected.

Ideological study and training outside Indonesia had apparently played a key part in radicalising those involved.

Growing concern about international support, including funding, of radical Islamic groups in Malaysia, Indonesia and the Philippines, have forced the region's governments to take a more co-ordinated approach to tackling the issue.

When Hambali, the man accused of forging practical links between al Qaeda and South East Asian groups, was arrested in Thailand last year, Thailand too found itself drawn further into the equation.

The current violence in the south may well be criminal, not fuelled by religious ideology.