LONDON, May 3 -- King Charles III's US state visit was a "risk and challenge" that he "grasped in both hands", a palace aide said today as the monarch returned from a widely praised trip.

Charles left for the UK from Bermuda yesterday following what a senior royal aide called a "historic" visit to the United States, aimed at healing strained ties between Washington and London.

The highlight of the four-day visit was the 77-year-old king's speech to US Congress on Tuesday - the first such address since his mother, queen Elizabeth II spoke there after the Gulf War in 1991.

The speech, marking 250 years since American independence, was "high stakes", the aide involved in the visit told reporters.

The king urged the importance of Nato and...