Google has banned smartphone maker Huawei from some updates on its Android operating system.
The search giant confirmed it was complying with a US government order blacklisting the Chinese firm.
Google said it was "complying with the order and reviewing the implications", but assured Huawei users that their current phones would continue to work.
Last week, US president Donald Trump signed an executive order effectively banning the Chinese firm from using US technology without government permission.
WHAT DOES THE BAN MEAN FOR HUAWEI USERS?
Huawei smartphone users will be able to update apps and get the latest security fixes.
They will also be able to update Google Play services.
However, Google is launching the new version of Android later this year and it may not be available on Huawei smartphones.
There are fears that future Huawei devices will no longer have Google apps such as YouTube and Maps.
"For users of our services, Google Play and the security protections from Google Play Protect will continue to function on existing Huawei devices," a Google spokesman said.
The block is likely to prevent future updates to Android reaching Huawei devices.
Key Google apps such as the Google Play Store, Gmail and Google Maps may also not appear on future Huawei devices.
Instead, the Chinese firm would be reliant on the version of Android available through an open source licence, which is vastly more limited in its features.
“SIGNIFICANT IMPACT” TO HUAWEI USERS
Huawei users have been warned they will be "significantly impacted" by Google restricting the Chinese firm's access to its Android software.
Industry expert Tristan Rayner, senior editor with the Android Authority news website, said the block means security updates to Huawei phones from Google will stop, and that buying a Huawei phone is now a "real risk".
"Existing Huawei device owners will be significantly impacted," he said.
"Whether it's someone with a brand new Huawei P30 Pro, which was unveiled last month, or the owner of an older Huawei Mate device that's a few years old, it's now clear that their Android operating system will no longer receive important security updates.
"Google's engineers are now forbidden to collaborate with Huawei engineers on these important updates. Google has said that users can still access the Google Play Store, and all the usual Google apps like Gmail, Google Maps, Search, Assistant, and so on.
"Therefore, while there will be some disruption, we do have some reassurances from Google that it isn't going to leave owners with a brick, effectively."
But, despite the assurances, Mr Rayner warned that buying future Huawei phones would be a "real risk" under the restrictions.
"Future Huawei devices will be significantly affected. We now know that future devices cannot be loaded with the Google Play Store, or those Google apps like Gmail or Google Maps," he said.
CAN HUAWEI USERS RETURN THEIR DEVICES?
Kate Bevan, editor of Which? Computing, said some recent purchasers of Huawei devices could consider returning their phones.
"It's unacceptable for consumers to be left without adequate security on their mobiles and Huawei owners will be seeking urgent reassurance that the safety of their devices will not be compromised," she said.
"In this situation, your consumer rights are limited as there's currently nothing faulty with these phones. However, if you purchased a phone in recent weeks it may be worth checking the retailer's returns policy."
HOW WILL IT AFFECT HUAWEI’S SALES?
Industry analyst Ben Wood from CCS Insight said the cut-off could have "considerable implications" for Huawei's gadgets business.
"We still don't have a clear understanding of what Google has told Huawei and what elements of the Android operating system may be restricted, so it remains unclear what the ramifications will be," he said.
"However, any disruption in getting updates to the software or the associated applications would have considerable implications for Huawei's consumer device business.
"People who currently own Huawei smartphones do not need to worry. At present any measures would only affect future devices and future updates. Google has publicly stated that its App Store, Google Play, and security updates from Google Play Protect will continue working on existing Huawei devices.
"However, until we have a clear understanding of what exact measures Google has decided to take it is impossible to second-guess the impact on future devices."
WHAT ABOUT HUAWEI’S OWN OS?
Huawei has previously confirmed it has been working on its own mobile operating system for use in the event of such blocks, something Mr Wood said now appeared likely.
"Huawei has been working hard on developing its own App Gallery and other software assets in a similar manner to the work it has done on developing its own chipsets for phones," he said.
"There is little doubt these efforts are part of its desire to control its own destiny.
"Last year, CCS Insight predicted that tensions between China and the US would present a strong incentive for Chinese companies to create their own operating system for smart devices. Given recent developments that seems more likely than ever."
HOW DID HUAWEI REACT?
"Huawei has made substantial contributions to the development and growth of Android around the world," the Chinese company said in a statement.
"As one of Android's key global partners, we have worked closely with their open-source platform to develop an ecosystem that has benefited both users and the industry.
"Huawei will continue to provide security updates and after sales services to all existing Huawei and Honor smartphone and tablet products covering those which have been sold or are still in stock globally.
"We will continue to build a safe and sustainable software ecosystem, in order to provide the best experience for all users globally."