Wales’ Brexit minister Jeremy Miles has urged the UK government to give “clarity and commitment” that EU funding will be fully replaced.
UK ministers have vowed to substitute the £375m that Wales gets annually from the EU, but have not confirmed how.
Mr Miles said there was “no time to lose”. The Welsh Government wants to keep control of the cash but a Tory MP said it could be spent better.
The UK government said it was committed to the devolution settlement.
Large parts of Wales received extra cash from the EU in the form of economic aid but the funds have been administered by the Welsh Government.
The UK government has promised a new Shared Prosperity Fund (SPF) to replace the money, which has continued to be paid under the transition period that ends in December.
The Conservative general election manifesto promised the replacement would match the size of EU funds “at a minimum”.
Under EU structural funds Wales would have received more than £5bn by 2020.
David Jones, Conservative MP for Clwyd West and a former Brexit minister, has called for the SPF to be run from Westminster, while Prime Minister Boris Johnson said last year there should be “strong Conservative influence” over how the cash is spent.
Mr Miles told BBC Wales: “I’d urge them to bring forward a clear commitment that there won’t be a penny less for Wales, and the devolution boundary will be respected.
“We haven’t yet had from them the level of clarity and commitment that we would expect.
“There is really no time to lose for this. We are in a situation where these programmes ought to be in place at the beginning of next year, and so really we need to be getting on with it,” he said.
Mr Miles spoke as the Welsh Government launched a consultation on its own proposals.
It has set out four priorities for investment – business productivity and competitiveness, reducing income inequalities, healthier and more sustainable communities, and a zero-carbon economy.
Stephen Crabb, Conservative MP for Preseli Pembrokeshire and chair of the Welsh affairs committee, said too often EU funds to Wales were spent “wrongly”.
“I don’t think there was enough focus on strategic infrastructure. I don’t think businesses were closely involved enough in the design and spending decisions previously, so we have an opportunity to rectify all of that.
“I don’t want to see any less money coming to Wales but I want to see the pot of money being spent better.”
In response Mr Miles said he did not accept the use of EU funds had not been effective – “quite the opposite”, he said.
But he added: “There’s always room to learn and do better in the future, and there are flexibilities which we can take advantage of in how we design some of these programmes… which help us with spreading geographically across Wales.”
‘Positive working relationship’
A UK government spokesman said: “The UK Shared Prosperity Fund will tackle inequalities between communities by raising productivity, especially in those parts of our country whose economies are furthest behind.
“The UK government remains committed to respecting the devolution settlement and working closely with the Welsh Government to ensure that the fund delivers for the people of Wales.
“The secretary of state for Wales has also reaffirmed his commitment to the positive working relationship which exists between both governments in Wales.”