See latest pictures of the iPhone 4

Apple Inc unveiled a new iPhone on Monday that goes on sale in scores of countries this year, preparing its fastest-ever global roll-out to try and stay a step ahead of rivals like Google Inc in a red-hot smartphone market.

CEO Steve Jobs showed off a redesigned $199 "iPhone 4" that is a quarter slimmer than the current handset. The device boasts a higher quality screen and better battery life, video chat via Wi-Fi, and a gyroscope sensor for improved gaming.

A slim but energetic Jobs told a media and industry audience at Apple's annual developers' conference in San Francisco that the latest phone will be available June 24 in five countries, expanding to 18 by July and 88 by September in the quickest-ever international roll-out for an iPhone.

That signaled how serious Apple is about gaining traction abroad, where iPhone penetration is still relatively small.

Despite the iPad's success in its first two months on the market -- more than 2 million sold in 60 days -- the iPhone remains Apple's main growth line, and the international market is key. Some analysts estimate more than two-thirds of iPhone sales are now coming from overseas.

"It's really just a huge market unit opportunity abroad for the iPhone," Broadpoint Amtech analyst Brian Marshall said.

But many of the innovations on the iPhone 4 had been expected, and industry watchers say it is becoming more difficult to stand out in a crowded field.

Google's Android operating system -- used by many brands from Motorola Inc and HTC Corp to Samsung Electronics Co Ltd and Dell Inc -- poses the biggest threat, analysts say.

The iPhone's global share surged to more than 15 percent in the first quarter, making it No. 3 in smartphones. Phones based on Android ranked No. 4 with close to 10 percent of the market, a huge increase from the previous year and gaining, Gartner data shows.

"There was nothing earth-shattering about what we saw or heard today," said CCS insight analyst John Jackson. "All of that said, you can't think it will be anything other than a phenomenal success."

Hudson Square Research analyst Daniel Ernst called the new device "more evolutionary than revolutionary."

"It doesn't completely change the paradigm for the iPhone," he said.