Amazon has reported it had weaker profits over the Christmas holidays, although a 15% rise in sales kept investors happy.

In the last three months of 2014 Amazon made a net profit of $214 million (£142 million) a fall of $25 million on the same period in 2013. The news comes despite net sales of £89 billion.

In a statement the company said: profits may be "materially affected by many factors, such as fluctuations in foreign exchange rates, changes in global economic conditions and consumer spending, world events, the rate of growth of the Internet and online commerce".