Posters have been going up in the Saudi Arabian capital, Riyadh, saying it is heresy under Islam to hold parties and give presents on birthdays.

The posters are copies of a religious decree issued three years ago by the country's top religious leader, Sheikh Abdulaziz bin Baz.

The decree adds that the same prohibition applies to companies and institutions marking anniversaries.

Religious decrees in Saudi Arabia normally carry the endorsement of the ruling family.

But the BBC Gulf correspondent says there is mounting speculation that this publication could be timed to embarrass the government.

Nationwide celebrations are due later this month to celebrate the centenary of the conquest of Riyadh by the nation's founding father, King Abdulazid al-Saud.

But some people say the posters were aimed at Christian expatriates in Saudi Arabia, who have been privately celebrating Christmas and New Year.