The website iMore, citing "sources familiar with the plans," said the 5S will retain the form factor and size of the iPhone 5 but will be equipped with an improved camera and an advanced processor.
The source also said Apple could also be releasing an updated line of iPads, including an iPad 5 and a second generation of the smaller iPad Mini even earlier, possible in April, PC Magazine reported Tuesday.
Although many Apple watchers have assumed the next iPad Mini would come with the high-definition Retina display, the source said that would not be the case.
One analyst, Ming-Chi Kuo of KGI Securities, said the new iPhone could be timed with the release of the iOS 7 operating system and may include a fingerprint identification component.
He reported a possible July debut and said Apple's apparently accelerated release schedule could be "an effort to avoid repeating the fatal mistake of last year of the delayed iPhone 5 launch, which gave competitors room to grab market share."
There have been rumors of a low-cost iPhone to be introduced at the same time, but Apple head Tim Cook has suggested the company would continue to offer the iPhone 4 and 4S as a low-cost alternative and as an entry into developing markets.