Two men identified by Thai police as "persons of interest" in the Bangkok shrine bombing have handed themselves in for questioning and reportedly said that they were tour guides.

The pair attracted police attention as they were seen in security camera footage near the man who appeared to leave a back-pack containing the bomb at the Erawan shrine.

The men stood up from a bench, leaving the space where the chief suspect sat down. And the duo then stood in front of the suspect as he left his bag under the bench, possibly shielding him from view, before leaving the scene at the same time.

They were being questioned on Thursday night in Bangkok after coming forward to explain that they were tour guides, the BBC reported. They insisted they had no connection to the atrocity.

There were strong indications that they had no involvement in the bombing which claimed the lives of at least 20 Thais and Asian tourists.

Police said that subsequent surveillance video footage showed that the two men had reacted with fear and shock when the bomb detonated, indicating that they had no idea that an explosion was expected.

Thai police chiefs have said that they believe that the chief suspect was part of a network of at least 10 people including both Thais and foreigners.

But on a day of mixed messages from the police and military rulers, Col Winthai Suvaree, a junta spokesman, also said that the bombing was not believed to be the work of an international terror group.

With no sign that arrests were close, Thailand also appealed on Thursday for help from Interpol to track down the main suspect, who they believed to be of "Caucasian, Arab or mixed race".

The assertion by the Thai authorities that the bomber was a foreigner and part of a network, but not linked to a global terrorist faction, only fuelled the mystery about the motives for the attack or who committed it.