British Prime Minister Rishi Sunak on Wednesday announced a world-first summit on artificial intelligence, seeking a leading role for the UK in limiting potential doomsday risks as he visited Washington.

Sunak will meet President Joe Biden at the White House on Thursday for talks during which he will also voice unstinting support for Ukraine, as the young Conservative leader wages an often uphill battle to show the UK's post-Brexit relevance.

Opening his two-day trip, the prime minister announced that Britain would hold the world's first summit on artificial intelligence in the second half of the year.

"AI has an incredible potential to transform our lives for the better. But we need to make sure it is developed and used in a way that is safe and secure," Sunak said.

"Time and time again throughout history we have invented paradigm-shifting new technologies and we have harnessed them for the good of humanity. That is what we must do again," he added.

The Group of Seven called for action on AI during a summit in Japan last month.

But the United States also held talks last week on an AI code of conduct with the European Union. Sunak is pitching for a future global AI regulator to be based in London.

"The UK is well placed to play a leadership role. Outside of the US, we are probably the leading AI nation amongst democratic countries. We have an ability to get regulation right to protect our citizens," Sunak told TalkTV.

- 'Ultimate sacrifice' -

Sunak opened his two-day US visit by laying a wreath at the Tomb of the Unknown Soldier at Arlington National Cemetery, with soldiers firing a 19-gun salute.

"In memory of those who made the ultimate sacrifice in order that we might live free. We will remember them," said a hand-written message from Sunak on the wreath.

The Ukraine war is expected to dominate his conversations with Biden, with Britain joining the United States in championing robust military support to Kyiv.

The visit comes as Russia and Ukraine trade accusations over who blew up the large Kakhovka dam, triggering devastating floods.

Any intentional targeting of the dam would represent "the largest attack on civilian infrastructure in Ukraine since the start of the war, and just would demonstrate the new lows that we would have seen from Russian aggression," Sunak told reporters aboard his plane from London.

The United States and Britain have not yet identified a culprit.

But in an interview with ITV News, Sunak said that Russia has pursued a "deliberate strategy to target civilian infrastructure."

"It is wrong, it's barbaric, and it's appalling. That's why we're providing such strong support to them and will continue to do so," he said of the Ukrainians.

Sunak has also been talking up British Defense Secretary Ben Wallace as a candidate to lead NATO before the Western military alliance holds a summit next month in Lithuania, with the prime ministers of Denmark and Estonia also seen as contenders.

NATO Secretary General Jens Stoltenberg's term in the job is due to end in October.

- Keeping hopes on business -

A day before meeting Biden, Sunak met Washington's top Republican, House Speaker Kevin McCarthy, who lauded the longstanding alliance.

"When our bond is stronger, the world is safer and democracy grows," McCarthy said.

Despite broad US support for Britain, Sunak has all but given up on a post-Brexit trade deal from the Biden administration, which has shown limited enthusiasm.

Sunak pointed to the US-UK military alliance as he made a case for the economic relationship.

"Just as interoperability between our militaries has given us a battlefield advantage over our adversaries, greater economic interoperability will give us a crucial edge in the decades ahead," said Sunak, a wealthy former banker who studied in the United States and retains a property in California.

The prime minister is pushing for US relief to UK carmakers, via greater access to critical minerals used in batteries, after Biden's Inflation Reduction Act offered vast subsidies to companies with US operations.

Sunak was due later to watch the Washington Nationals baseball team play the Arizona Diamondbacks for the second annual "UK-US Friendship Day," marking 238 years of diplomatic relations.

But the keen cricketer ducked the opportunity to throw the ceremonial first pitch -- sparing his blushes if the throw goes astray in front of thousands.

 AI chatbots offer comfort to the bereaved

Staying in touch with a loved one after their death is the promise of several start-ups using the powers artificial intelligence, though not without raising ethical questions.

Ryu Sun-yun sits in front of a microphone and a giant screen, where her husband, who died a few months earlier, appears.

"Sweetheart, it's me," the man on the screen tells her in a video demo. In tears, she answers him and a semblance of conversation begins.

When Lee Byeong-hwal learned he had terminal cancer, the 76-year-old South Korean asked startup DeepBrain AI to create a digital replica using several hours of video.

"We don't create new content" such as sentences that the deceased would have never uttered or at least written and validated during their lifetime, said Joseph Murphy, head of development at DeepBrain AI, about the "Rememory" program.

"I'll call it a niche part of our business. It's not a growth area for us," he cautioned.

The idea is the same for company StoryFile, which uses 92-year-old "Star Trek" actor William Shatner to market its site.

"Our approach is to capture the wonder of an individual, then use the AI tools," said Stephen Smith, boss of StoryFile, which claims several thousand users of its Life service.

Entrepreneur Pratik Desai caused a stir a few months ago when he suggested people save audio or video of "your parents, elders and loved ones," estimating that by "the end of this year" it would be possible to create an autonomous avatar of a deceased person, and that he was working on a project to this end.

The message posted on Twitter set off a storm, to the point where, a few days later, he denied being "a ghoul."

"This is a very personal topic and I sincerely apologize for hurting people," he said.

"It's a very fine ethical area that we're taking with great care," Smith said.

After the death of her best friend in a car accident in 2015, Russian engineer Eugenia Kyuda, who emigrated to California, created a "chatbot" named Roman like her dead friend, which was fed with thousands of text messages he had sent to loved ones.

Two years later Kyuda launched Replika, which offers personalized conversational robots, among the most sophisticated on the market.

But despite the Roman precedent, Replika "is not a platform made to recreate a lost loved one", said a spokeswoman.

- 'Philosophical' -

Somnium Space, based in London, wants to create virtual clones while users are still alive so that they then can exist in a parallel universe after their death.

"It's not for everyone," CEO Artur Sychov conceded in a video posted on YouTube about his product, Live Forever, which he is announcing for the end of the year.

"Do I want to meet my grandfather who's in AI? I don't know. But those who want that will be able to," he added.

Thanks to generative AI, the technology is there to allow avatars of departed loved ones to say things they never said when they were alive.

"I think these are philosophical challenges, not technical challenges," said Murphy of DeepBrainAI.

"I would say that is a line right now that we do not plan on crossing, but who knows what the future holds?" he added.

"I think it can be helpful to interact with an AI version of a person in order to get closure —particularly in situations where grief was complicated by abuse or trauma," Candi Cann, a professor at Baylor University who is currently researching this topic in South Korea.

Mari Dias, a professor of medical psychology at Johnson & Wales University, has asked many of her bereaved patients about virtual contact with their loved ones.

"The most common answer is 'I don't trust AI. I'm afraid it's going to say something I'm not going to accept'... I get the impression that they think they don't have control" over what the avatar does.