A “partnership” with Westminster, Wales’ politicians and councils will decide how replacement EU cash is spent, Welsh Secretary Simon Hart says.
But Plaid Cymru said devolution will “exist in name only” with the UK government accused of “siphoning money away from our poorest communities”.
Liz Saville-Roberts was responding as further details of a new Shared Prosperity Fund (SPF) were made public.
It replaces European Commission development and social fund grants.
Mr Hart said Westminster “intend to work alongside” ministers and councils.
“The idea is that this is going to be much more of a partnership effort than it’s ever been before,” he said.
“And not just a partnership by the way between politicians and Westminster and Cardiff.
“Local authorities and many more people are going to be involved in this.”
Money used to move from Brussels to devolved nations like Wales with aid administered by the Welsh Government.
But, in a letter to the Scottish finance secretary, UK Treasury Secretary Stephen Barclay has said the Shared Prosperity Fund would be a UK project, help “levelling up” areas most in need.
Ms Saville Roberts, Plaid’s Westminster party leader, said: “First a power grab, now a funding grab. Hot on the heels of the ruinous Internal Market Bill, this is another shameless Tory attack on devolution.
“They’re siphoning money away from our poorest communities, and unless we stop them, devolution will exist in name only.”
Examples of where EU money was spent in Wales include colleges and roads, such as the Heads of the Valleys.
Following Brexit, ministers in the devolved countries and Westminster have been arguing over who should control the cash, with First Minister Mark Drakeford saying any attempt to centralise control over funding in London would be an “attack on devolution”.
However, in his letter, Mr Barclay confirmed European structural funds will be replaced with a centrally-controlled system.
He said: “The UK SPF will help to level up and create opportunity across the UK in places most in need.
“It will operate UK-wide, using the new financial assistance powers in the UK Internal Market Act.
“We will ramp up funding so that total domestic UK-wide funding will at least match EU receipts on average reaching around £1.5bn a year.”
Responding, a Welsh Government spokeswoman said it was “not appropriate” for the UK government to “involve itself with clearly devolved matters”.
“The SPF should be run in Wales, much as the EU Funds it replaces have been,” she added.
The spokeswoman said a framework for regional investment was published in November outlining how the SPF would be used in Wales.”It is disappointing that the UK government has neither provided the promised funding to replace the EU funds nor given any clear indication of how it sees the SPF working in devolved administrations, other than to suggest that it intends to ignore the clear consensus in Wales on how the funds should be deployed that is set out in our framework,” she added.