SAN FRANCISCO - Apple on Monday announced that it has sold more than four million of its new iPhone 4S, three days after the launch last Friday.

"IPhone 4S is off to a great start with more than four million sold in its first weekend - the most ever for a phone and more than double the iPhone 4 launch during its first three days," said Philip Schiller, Apple's senior vice president of worldwide product marketing.

In addition, more than 25 million customers are already using iOS 5, the latest version of the mobile operating system powering Apple's mobile devices, since it was released last Wednesday; and more than 20 million customers have signed up for iCloud, the cloud service designed to store and sync data for download to multiple devices, said the company in the statement.

The iPhone 4S, which looks the same as the iPhone 4, has major hardware upgrade inside, including a faster chip, a higher-resolution camera and Siri intelligent voice control.

Last Friday, AT&T and Sprint, two iPhone wireless carriers in the United States, said they have seen record daily sales with the launch of the iPhone 4S.

The lasted Apple smartphone is currently on sale in the US, Canada, France, Germany, Japan and Britain, and will be available in 22 more countries on October 28. Apple said the phone will be on sale in more than 70 countries and regions by the end of this year.