The announcement is Starmer's latest effort to protect children from the harmful impacts of technology.
It comes as the Times reported that he is also planning to announce a ban on some social media platforms for those aged under 16.
"Today I'm calling on tech companies operating in this country to introduce device controls that prevent children from sending and receiving sexually explicit images," Starmer said in a speech at London Tech Week on Monday.
"This is not an impossible challenge."
Under the new plans, firms such as Apple and Google would have to build or activate technical solutions on smartphones and tablets to detect and block nude images for children.
Adults would still be able to take, share or view nude content through an age verification process.
If companies did not act within three months, the government said it would bring forward legislation to force them to do so or risk facing fines or, as a last resort, the threat of criminal liability for bosses.
Google said it was deeply committed to protecting children online.
"We are working constructively with UK partners to find effective, privacy-preserving solutions that deter the spread of harmful content while ensuring a safe digital environment for young people," a Google spokesperson said.
Apple did not comment. The company has tools designed to limit children's exposure to explicit content, including a feature that warns when nudity is detected in images sent or received.
The British authorities said blocking nudity was key, saying it would disrupt much of the grooming and sextortion model of gangs and predators who share nude images with others or use them to blackmail minors.
They argue it is technically achievable and can be done quickly.
At present, a child sex abuse referral is made about every five minutes, with 91 per cent of images self-generated.
The government said it wanted to work with industry and that age checks recently introduced by Apple were a significant step forward.
But it wanted more action by both Apple and Google to block nudity by default and across third-party apps.
Britain has separately been considering whether to ban children from accessing social media in response to widespread concern about its overall safety and the impact it has on mental health.
Australia in 2025 blocked children under 16 from platforms including TikTok, Alphabet's YouTube and Meta's Instagram and Facebook.
France, Denmark and Poland are also considering tightening rules around social media use for children, while Greece in April announced it would ban access to those under the age of 15 from January 2027.
