Monday's bombing in Thailand was "unlikely" to have been masterminded by an international terror group, the Thai government has said.

This was the preliminary conclusion reached by investigators according to the spokesman for the ruling military junta; Col. Winthai Suvaree.

Authorities however say the prime suspect in the bombings was foreign. The attack on the Erawan Shrine in central Bangkok on Monday evening killed 20 people and injured scores.

Police say that at least 10 people are suspected of involvement in the attack.

National police chief Somyot Pumpanmuang said he believed the attack was planned at least a month in advance.