Brexit: Theresa May meets Irish PM Enda Kenny in Dublin
Theresa May has said she wants to see a "seamless, frictionless border" between Northern Ireland and the Republic of Ireland after the UK leaves the EU.
The prime minister made her comments after discussing the implications of Brexit with her Irish counterpart Enda Kenny in Dublin on Monday.
The Irish border is one of the most critical issues for her government to handle during Brexit negotiations.
Mr Kenny said a "friction-free" trade link would be vital for both countries.
There are fears that a so-called hard Brexit could see the introduction of controls on movement and trade between the countries.
'Free movement essential'
The Irish prime minister said he made it clear to Mrs May that "any manifestation of a hard border" would have "very negative consequences that [Mrs May] fully understands".
Mrs May said she understood that the ability of people to move freely across the Irish border is "an essential part of daily life".
"We need to find a solution which enables us to have as seamless and frictionless a border as possible between Northern Ireland and Ireland so that we can continue to see the trade, the everyday movements that we have seen up to now," she added.
The prime ministers said they also discussed the political crisis in Northern Ireland that has led to the calling of an assembly election.
Mrs May said the difficulties faced by the institutions at Stormont were "serious".
"It is fundamentally important that we work with Northern Ireland's political leadership to find a solution," she said.
After the talks, Mr Kenny said he intended to accept an invitation from Donald Trump to visit the White House on St Patrick's Day despite the US president's controversial immigration crackdown.
He said he disagreed with Mr Trump's immigration policy banning citizens from Iraq, Syria, Iran, Libya, Somalia, Sudan and Yemen from entering the US.
But Mr Kenny added that it was important to "say face-to-face to the president the issues that are of importance to us".
"I don't want a situation where 35 million Irish-Americans or the 50,000 undocumented Irish who are in the States are left without contact or connection during St Patrick's week," he said.
"We have had great influence in the US over the years - we still have that influence and we intend to use it."
Earlier, Mrs May met leaders and ministers from the UK's three devolved governments at a summit in Cardiff.
The representatives from Northern Ireland, Scotland and Wales pressed her for a greater role in Brexit negotiations with the EU and Mrs May told them she would "intensify" work on their proposals for the talks on the UK's withdrawal from the EU.