(AFP) - US President Joe Biden on Wednesday began a nostalgia-filled tour of the Republic of Ireland, jetting in from Northern Ireland where he pushed for an end to crippling political paralysis in the British province.

Biden emerged from Air Force One at Dublin airport to driving wind and rain, and was greeted by the Irish Taoiseach (prime minister) Leo Varadkar and a sea of black umbrellas.

The 80-year-old president, who regularly mentions his Irish roots, calls Ireland "part of my soul" and his visit includes trips to the hometowns of his 19th-century ancestors.

He will also meet Irish head of state Michael Higgins and address a joint sitting of both houses of the Oireachtas -- the Irish parliament -- before heading home late Friday.

Despite the sentimental nature of his Irish visit, Biden was keen to underscore the seriousness of his trip.

The priority, he said, was "to keep the peace" in Northern Ireland, 25 years after a landmark peace agreement that ended three decades of deadly sectarian violence over British rule.

He used a speech at a new campus of Ulster University in Belfast earlier on Wednesday to promote the benefits of enduring peace and investment.

But he still faced heated criticism from pro-UK hardliners.

The UK government also downplayed suggestions his one-night-only trip to Belfast was a snub to the so-called "special relationship".

"I hope the (Northern Ireland) Executive and Assembly will soon be restored," Biden said, urging feuding leaders to restore power-sharing government which has been suspended since February last year.

- 'Anti-British?' -

Biden touted the "unlimited possibilities" for investment and growth offered in Northern Ireland, 25 years on from the Belfast/Good Friday Agreement.

But, he said, peace and stability must always be guarded, warning that the January 6, 2021, riot at Congress in Washington had proved that in every generation, "democracy needs champions".

The president met Prime Minister Rishi Sunak, who said the UK's relationship with the United States was "in great shape" and greeted local political leaders.

Senior figures in the pro-UK Democratic Unionist Party (DUP), which is under pressure to resume local power-sharing, were strikingly undiplomatic about the president.

Sammy Wilson, a DUP member of the UK parliament in Westminster, branded Biden "anti-British", accusing second Catholic US president of having "made his antipathy towards Protestants in particular very well known".

Another DUP lawmaker, Nigel Dodds, called Biden's administration "transparently pro-nationalist" while party leader Jeffrey Donaldson said the visit did nothing to change the political dynamic.

Power-sharing government is a key plank of the 1998 peace accord, but it collapsed 14 months ago over the DUP's opposition to post-Brexit trade arrangements in Northern Ireland.

The party fears that keeping Northern Ireland in the European single market and customs union drives a wedge between the province and Great Britain (England, Scotland and Wales).

Despite the UK and the European Union agreeing to overhaul trading rules earlier this year, the DUP is yet to back the new trading terms and allow the restoration of Belfast's Stormont legislature.

- Security fears -

Biden's defenders hit back at claims he was "anti-British".

"The president has been very actively engaged throughout his career, dating back to when he was a senator, in the peace process in Northern Ireland," said Amanda Sloat, National Security Council Senior Director for Europe.

Sectarian violence remains a concern north of the border, 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 had been retrieved from a cemetery in the Creggan area of the city.

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

The five-star hotel in Belfast where he stayed 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.

"I came here in '91 to this neighbourhood and you couldn't have a glass building like this here... I don't think they would have stood up very well," Biden said of the new university campus.

"The dividends of peace are all around us."

© Agence France-Presse