Bangkok shrine bomb: Who could be behind deadly attack?

A bomb has exploded close to a shrine in the centre of Thailand's capital, Bangkok, killing at least 19 people and injuring more than 120.

The Erawan Shrine, which was crowded at the time, is a major tourist attraction and foreigners, including Chinese, are among the casualties.

With the Thai government saying it does not know who is to blame, and no group claiming responsibility, Bridget Kendall looks at who could be behind the attack.