Many Muslims around the world have begun fasting and prayers to mark the holy month of Ramadan.

In a Ramadan message, President Obama expressed his warmest wishes to Muslim Americans and Muslims around the world. He also hailed the courage of those fighting for democracy in the Islamic world.

The president's message came amid continuing fighting in Syria between rebels and pro-government forces. In Thailand, Ramadan was marred by attacks that killed at least one person and injured at least four. The attacks took place in southern Thailand, where most of the country's Muslims live and which has been the scene of insurgent violence.

The start of Ramadan varies because Muslims use different ways of calculating when the new moon crescent is sighted.