LONDON, May 16 (Reuters) - Shares in Sage group fell to a six-month low on Thursday after the British software group trimmed its full-year revenue forecast on expectations of lower growth in the United States.

Chief Executive Steve Hare told analysts that Sage had "slightly more modest" expectations around U.S. growth in the second half, but it was seeing "probably slightly stronger growth in Europe".

In its first-half results statement on Thursday, Sage said it expected its full-year growth to be broadly in line with the 9% recorded in the six months to end-March, down from growth in line with last year's 10% it forecast in November.

Shares in Sage were trading down 9% at 1,085 pence by 1140 GMT on Thursday, the worst performer in the FTSE 100 index.

The company, which provides accountancy software to small and medium-sized businesses, reported an 18% rise in underlying operating profit to 254 million pounds ($321.7 million) in the period after it increased its margin by 1.6 percentage points to 22%.

Hare said Sage had seen a very positive response to the recent introduction of Sage Copilot, its generative AI-powered digital assistant.

The company had given more than 1,000 demonstrations of Sage Copilot to potential customers on the first day of the Accountex London trade show on Wednesday, he said in an interview.

($1 = 0.7896 pounds) (Reporting by Paul Sandle. Editing by Jane Merriman)