Apple has sold 450,000 iPads and 600,000 electronic books have been downloaded for the new tablet computer, Apple chief executive Steve Jobs said Thursday.

"We're making (iPads) as fast as we can," Jobs said at the start of an event at Apple headquarters here during which the company is to unveil the latest operating system for the iPhone.

"Evidently we can't make enough of them yet so we are going to have to try harder," Jobs said.

The Apple chief executive also said that iPad owners have downloaded 3.5 million applications for the iPad as of Thursday.

Apple sold over 300,000 iPads on Saturday, its first day of availability in the United States, and Jobs said 450,000 of the touchscreen multi-media devices had been sold as of Thursday.