The market share of Apple Inc's (AAPL.O) iPhone declined in key regions in the three months ended October, hurt by the unavailability of the iPhone X during that time, research firm Kantar Worldpanel ComTech said on Tuesday.

In the United States, the share of iOS - the iPhone's operating system - declined to 32.9 per cent from 40.6 per cent a year ago, data from Kantar showed.

IOS share also fell in Japan and big European markets, while Google's Android gained share in most markets, Kantar said.