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Mobile phone giant Nokia has reported a loss for the final three months of last year, as sales of mobile devices fell sharply.

The firm made loss after tax of 1.08bn euros ($1.4bn; £905m). Net sales fell 21% on a year earlier to 10bn euros.

Net sales of mobile phones were down by a quarter.

In October, Nokia launched its first two Windows-based smartphones which it hopes will help it gain ground on Apple and Android-based competitors.

"The fourth quarter of 2011 marked a significant step in Nokia's transformation," said chief executive Stephen Elop.

"Overall, we are pleased with the performance of our mobile phones business."

The former market-leader in mobile phones has lost out to the iPhone and other smartphones that use Google's Android operating system.

To try to catch up, it decided to dump its legacy Symbian software in favour of Microsoft for its new range of smartphones.

It launched the Lumia 800 and Lumia 710 models in October in a number of markets in Europe and Asia, and earlier this month re-entered the US market. It has now sold more than one million Lumias.

Nokia said it would be launching the new smartphone models in China and Latin America in the first half of this year.

The company said 2012 would continue to be a "year of transition" so it would not be giving any sales or profits forecasts.

On Wednesday, Nokia said it had sold its 1.5 billionth mobile phone based on its S40 operating system.

It estimated there are currently 675 million active owners of S40 phones in the world, and said it is currently selling about 12 phones of the S40 family every second.