Donald Trump's renewed endorsement of a united Ireland left his Doonbeg visit shadowed by protests and a major security operation as he spent Sunday at Trump International Golf Links for the Irish Open.

Speaking after watching tournament leader Shane Lowry tee off, the president said it would be natural to put Ireland and Northern Ireland "together" and described his earlier remark as "a fairly routine comment." He added, "I've always loved the people of Ireland. It just seems to me you have Northern Ireland and Ireland. It seems that one of the naturals of all time is to put them together. That's only my opinion, and by the way many people agree."

He also sidestepped a question on Scottish independence, saying "I won't talk about Scotland yet I will save that."

Mr Trump had made an initial comment while meeting the Taoiseach Micheál Martin in Dublin on Saturday, telling reporters he would love to see a united Ireland. Mr Martin said the president's remarks did not come as a "surprise" and recalled Mr Trump asking about a possible "merger" of Northern Ireland and the Republic at a Saint Patrick's Day event in Washington.

A major security operation continued during the visit. More than 10,000 people marched through Dublin on Saturday to show opposition to the president, and about 100 protesters arrived in Doonbeg on Sunday. Gardaí moved a small crowd from the president's hotel and three women arrested for trespassing on the golf links appeared at a special sitting of Ennis District Court.

Voices in Doonbeg were divided. Rev Steven Foster, a Methodist minister from Galway who attended the anti-Trump protest, said, "I'm here because Trump is the exact opposite of everything I stand for as a follower of Jesus," adding the church needs to be visible on the issue. Local business owners defended the golf course: Martin Kelly called it "a massive employer" and Seoirse Comerford said there are "over 300 people employed up there at the golf course," describing the tournament as a "big boost" to the local economy.

The visit is due to end on Sunday evening when Mr Trump will leave from Shannon Airport, leaving a two-day trip that combined sport, business and a renewed spotlight on the future of the island.