The FTSE 100 was up 0.1% and the FTSE 250 was 0.3% higher by 0721 GMT.

Trump on Tuesday described the conflict as "a little squabble" and said talks between the world's two largest economies had not collapsed.

Asia-focussed HSBC provided the biggest boost to the main index, up 0.6%.

"A series of comments and tweets from the President has markets behaving a little more sensibly, but risks still seem skewed to the downside until there is clarity and a (trade) deal," Markets.com analyst Neil Wilson said.

On an earnings-heavy day, tour operator TUI was the biggest blue-chip gainer. It rose 2.8% after in-line half-year results, while warning that lack of clarity over the status of its grounded Boeing 737 MAX planes could hit profits.

The world's biggest catering firm Compass Group added 2.4% after hiking its annual organic revenue growth forecast.

On the mid-cap index, lender CYBG recorded a steep rise after it swung to a first-half profit. Shares jumped 8.8% and were on track for their best day in more than three months.