Every effort needs to be made to ensure there is no hardening of the maritime border between Ireland and Wales post-Brexit, the Welsh First Minister has said.
Carwyn Jones said that any customs deal on the border that was made between the north and south in Ireland should also apply for Wales.
He said he did not agree with Prime Minister Theresa May's handling of the Brexit talks and that it was not in the Irish or Welsh interest for there to be any extra bureaucracy that could hinder trade.
The comments were made after a planned meeting between Taoiseach Leo Varadkar and Mr Jones at Government Buildings in Dublin on Monday was cancelled.
The Welsh First Minister had been due to meet Mr Varadkar to discuss trade post-Brexit but it was cancelled to allow Mr Varadkar to travel to Stormont to take part in talks with Mrs May.
Mr Jones said he did not agree with the way Brexit has been handled by the UK Government.
"I don't agree with Theresa May," Mr Jones said.
"I think leaving the customs union has no sense at all, there are plenty of countries that are outside of the EU, but still in the customs union."
He added that Wales had always wanted full and unfettered access to the single market.
"It's in no one's interest for there to be extra bureaucracy and extra paperwork when goods are moved through the Irish ports into Wales," he said.
Mr Jones told RTE's Morning Ireland programme that if the Welsh people were asked what type of Brexit they wanted, he believed they would want a sensible one, not one driven by dogma.
"Unfortunately the UK Government has not played its hand at all well," he said.
"It started off saying it wanted a pretty hard Brexit and it has shown that it cannot be flexible.
"Well as far as we're concerned what is needed is not a Brexit driven by some strange flag-wielding nationalism in Westminster, but a Brexit driven by what's good for business and jobs in Wales and indeed the other countries of Britain."
Mr Jones said Welsh ports were dependent on trade from Irish ports.
"Our worry is that if, for example, the border between north and south here in Ireland is softer than the border, the maritime border between the Republic say and Wales, then there will be an incentive for freight to move into Belfast from Scottish and English ports, and avoid the Welsh ports," he said.
"Everyone wants to see the border between the north and south of Ireland to be as soft as possible but we want to make sure that applies for the border between the Republic of Ireland and Wales as well.
"Nobody wants to see there be any kind of physical manifestation of a border between north and south, nobody argues for that, but what I argue for is that if there's a seamless customs arrangement between north and south in Ireland there's no reason why that can't also apply in terms of goods that are moving across the sea into Wales."
Ports make a huge contribution to the Welsh economy, supporting around 11,000 jobs and providing an economic hub and trade gateway with Europe and the rest of the world.
About 80% of goods carried in Irish-registered HGVs between the Republic of Ireland and Europe pass through Welsh ports.