Biden touts peace and prosperity in restive N. Ireland

US President Joe Biden was set Wednesday to promote the potential of enduring peace as well as business investment on his trip to Northern Ireland.

Following a late-night greeting in blustery weather from UK Prime Minister Rishi Sunak, Biden's brief visit comes with the British-ruled territory again in the grip of political and sectarian squalls, 25 years on from a US-brokered peace agreement.

Biden was due to meet Sunak and Northern Ireland's feuding political leaders in Belfast before delivering a speech at a newly opened city-centre campus of Ulster University.

The Irish-American president, 80, will then head on to the Republic of Ireland for a trip down memory lane, encompassing visits to the hometowns of his 19th-century ancestors.

Before boarding Air Force One, Biden said the priority for his trip was "to keep the peace" in Northern Ireland and help unlock its political paralysis.

His delegation includes a scion of the Irish-American Kennedy clan, Joe Kennedy III, Biden's new special envoy for economic affairs in Northern Ireland.

Biden's visit will mark the "tremendous progress" since the Good Friday Agreement ended armed conflict between pro-Irish and pro-British militants in April 1998, according to the White House.

"We'd like to see the national assembly (in Belfast) returned, clearly," National Security Council spokesman John Kirby told reporters aboard Air Force One, with the Stormont legislature currently suspended.

"The message is twofold. It's congratulations on 25 years of the Good Friday agreement... (and) to talk about the importance of trying to work on trade and economic policies that benefit all communities as well as the United States," he said.

Biden is likely to press the pro-UK Democratic Unionist Party (DUP) to resume power-sharing at Belfast's Stormont assembly.

Devolved government in Belfast is a key plank of the 1998 accords, but it collapsed 14 months ago over the DUP's trenchant opposition to post-Brexit trade arrangements in Northern Ireland.

DUP leader Jeffrey Donaldson will urge Biden "to not make a political intervention but to encourage economic support", hardline DUP lawmaker Ian Paisley Jr told Britain's TalkTV.

Biden is already in campaign mode and playing up his Irish roots for US voters, Paisley said, noting the president would spend a full three days in Ireland.

"So I think we read into that, this is just a part of his campaign and we happen to be an opportunity along the road, we're nothing more than that," he said.

Sectarian violence remains a concern, with Britain's MI5 security agency elevating its terrorism threat level for the territory ahead of Biden's visit.

On Monday, masked youths pelted police vehicles with petrol bombs during an illegal march by hardline nationalists in Londonderry, which is also known as Derry.

Police in Northern Ireland on Tuesday said that four suspected pipe bombs were retrieved from a cemetery in the Creggan area of the city.

"All of these devices were located in the same area where clothes worn by participants in (Monday's) unnotified Easter parade were removed under the cover of umbrellas and burnt," officers said.

Biden has brushed off any security concerns, and will see up close how much redevelopment has transformed Belfast since 1998.

Biden's five-star hotel in Belfast only opened in 2018.

Before 1998, the only place for visiting dignitaries to stay was the nearby Europa, which was attacked so often by the Irish Republican Army paramilitary group that it became known as the most bombed hotel in Europe.