Apple on Tuesday acknowledged that an iPhone 6S shut-down problem is more widespread than first believed, and said it will include diagnostic tools in the next iOS update to collect more information on why some phones are shutting down unexpectedly.

As with the initial admission, yesterday's was posted on the Apple website for the People's Republic of China (PRC) in both Chinese and English. Apple has not repeated the disclosure on its U.S. site.

Apple's latest missive signaled that the Cupertino, Calif. company does not know why some iPhone 6S handsets are turning off on their own even though the battery indicator showed a third or more of the charge remaining.

Late last month, Apple confirmed that some iPhone 6S smartphones were turning themselves off without warning. At the time, it said the problem was limited to devices made in September and October 2015 -- during early, but likely not initial, production runs of the model -- and launched a global battery replacement program for eligible customers.

Yesterday, Apple again cited the battery as the root cause. "A small number of iPhone 6s devices ... contained a battery component that was exposed to controlled ambient air longer than it should have been before being assembled into battery packs," Apple asserted, as it did in a Dec. 1 post.

But customers with iPhone 6S phones whose serial numbers do not put them in the September-October 2015 production range have also watched their devices shut down, Apple said.

"Some of these shutdowns can occur under normal conditions in order for the iPhone to protect its electronics," Apple said, repeating a claim of last week in the first message. "In an effort to gather more information, we are including additional diagnostic capability in an iOS software update which will be available next week. This will allow us to gather information over the coming weeks which may potentially help us improve the algorithms used to manage battery performance and shutdown."

The update Apple mentioned will almost certainly be iOS 10.2, which has been in beta -- and refreshed seven times thus far, most recently Wednesday -- since Nov. 1.

Apple has been criticized by the China Consumer Association (CCA) -- an advocacy watchdog with ties to the government -- since mid-November over iPhone 6 and 6S shutdown problems. Last week, the CCA again took Apple to task, using a Nov. 30 announcement on its website (Chinese-language version) to accuse the American company of dragging its feet. The second message said the CCA had again sent a letter to Apple, contending that other models, including the iPhone 6 Plus and 6S Plus, had exhibited the shutdown behavior. The group also asked Apple for more information on the possible causes.

The inclusion of diagnostic capabilities in iOS 10.2 next week was probably a direct response to the CCA's demand.