The prime minister has said it is “up to the EU, this is their call” if the UK leaves the EU without a deal.
Boris Johnson made his first visit to Wales as PM on Tuesday, bidding for farmers’ support for his Brexit plans.
A Welsh farmer called on Mr Johnson to stop “playing Russian roulette” with the lamb industry over the threat of a no-deal Brexit.
But Mr Johnson said: “We’re not aiming for a no-deal Brexit, we don’t think that’s where we’ll end up.”
“This is very much up to our friends and partners across the channel,” he said.
It followed the Farmers’ Union of Wales president warning of “civil unrest” in rural areas if the UK leaves the EU without an agreement.
Earlier, the prime minister had his first phone call with Irish leader Leo Varadkar since taking office.
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The visit to Wales came as the Conservatives fight to hold Brecon and Radnorshire in a by-election on Thursday.
Mr Johnson visited a chicken farm in St Brides Wentlooge, near Newport, before travelling to online retailer BVG Group in Brecon.
He later attended discussions in the Welsh Assembly with First Minister Mark Drakeford, where he was booed by a group of protesters on arrival.
Many Welsh farmers are heavily reliant on free trade with the EU. If the UK leaves without a deal many would face significant tariffs on their exports to EU countries.
The prime minister did not give any television interviews to Welsh broadcasters on Tuesday.
However he told reporters the farming sector will “have the support they need” in the event of no-deal.
“We will make sure that they have the support that they need, if there are markets that are going to be tricky that we help them to find new markets, we have interventions that aim to support them and their incomes,” Mr Johnson said.
He said: “The most important point is that we don’t want tariffs and we don’t envisage they will be necessary.
“And I think common sense would dictate it would be better and massively in the interests of our EU friends to have a zero tariff zero quota regime of the kind we currently have.”
Mr Johnson suggested funds for “export refunds” would be made available for the Welsh Government to administer.
Asked how the system would work, given agriculture is devolved, he said: “It will be up to the Welsh Government to administer it. We will make sure the funds are available.”
A Welsh Government source said they were surprised by the nature of the announcement.
The farming industry is worth more than £6bn to the Welsh economy and supports 14,000 businesses, 45,000 jobs and about 25,000 farmers.
Welsh lamb will face at least 40% tariffs in a no deal scenario, prompting a sheep farmer to call for Mr Johnson “to stop playing Russian roulette with the industry as he appears to be doing at the moment”.
“If we do go out with a no deal, it will be absolutely catastrophic even if it is just for a few months,” Helen Roberts, who is also development officer for the National Sheep Association in Wales, told Radio 4’s Today programme.
She said her members will protest against a no-deal Brexit: “I think it’s time to come and stand up for ourselves, and be counted.”
On Monday, the prime minister said there was “every chance” a Brexit deal with the EU could be struck, but the existing agreement with the EU has “got to go”.
However senior minister Michael Gove, who has been put in charge of preparing for no deal, has said the UK government was working on the assumption the UK would leave the EU without an agreement.
Ahead of his meeting with Mr Johnson, Mr Drakeford said he would tell the PM: “Brexit will be catastrophic for Wales.”
He tweeted: “It will decimate our agricultural and manufacturing sectors & risks ripping the Union apart. The PM must stop playing fast and loose with our country.”
BBC Wales political editor Felicity Evans said the first minister “had been warning for a long time that a no deal was a catastrophe, now he’s stepped that up to say any Brexit would be”.
“We’ve seen the Welsh Government pivoting on Brexit since the European Parliamentary elections which were historically awful for Welsh Labour,” she added.
Mr Drakeford has thrown his weight behind a further referendum since that result.
In the 2016 EU referendum 52.5% of voters in Wales voted to leave the European Union while 47.5% wanted to stay.
Ahead of the visit Welsh Secretary Alun Cairns suggested new global markets, including in Japan, will be available to sheep meat producers.
Mr Cairns told the BBC: “We are now looking to the growth that will come from right around the world, 90% of global growth will come from outside of the EU,
“But we don’t want to close our back on the European market either and that’s why working hard to get a deal is important, but of course there needs to be a shift in attitude and a positive response to the cause that we’re making.”
Plaid Cymru Westminster leader Liz Saville Roberts pointed out via Twitter the Japanese market had been opened up to Welsh lamb by the EU-Japan trade deal.
Mr Cairns added farmers “can be guaranteed that the same money will be available to ensure that we are protecting this sector”.
No-deal Brexit up to the EU, says Boris Johnson on first Welsh visit}