US President Joe Biden landed in Northern Ireland on Tuesday, hoping to help maintain the fragile peace brokered 25 years ago after decades of sectarian violence over British rule.

Before boarding Air Force One, Biden, 80, said the priority for his trip was "to keep the peace" and bring an end to the protracted political deadlock caused by opposition among pro-UK parties to post-Brexit trading rules.

UK Prime Minister Rishi Sunak met Biden on the tarmac when he touched down in the Northern Irish capital, just 24 hours after the landmark anniversary of the Good Friday/Belfast Agreement.

But security remains a concern.

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

Despite the scenes, US officials said Biden was "very excited for this trip".

"We'd like to see the national assembly (in Belfast) returned, clearly," National Security Council spokesman John Kirby told reporters en route to Belfast, 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 will deliver remarks on Wednesday at Ulster University in Belfast, set to focus on the economic promise of inward investment if the peace endures.

He will also meet the leaders of Northern Ireland's main political parties, the White House said, with reports he will press the pro-UK Democratic Unionist Party (DUP) to resume power-sharing.

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

Biden, who has Irish ancestry, will also travel south to Ireland for a three-day visit, in part tracing his family history.

During a trip to County Mayo in northwest Ireland on Friday, Biden will visit his ancestral hometown of Ballina and meet distant cousins. (AFP)