"Unnecessary delays" over an application to mine gold in Co Tyrone are "harming" Northern Ireland's reputation, the US ambassador to the UK has said.
In a speech in Belfast, Warren Stephens said a decision needed to be made over the Dalradian gold mine project "fast", stating it could bring jobs and investment to the region.
In a strongly-worded address, the diplomat also said "bureaucracy must not become a barrier to progress" in Northern Ireland as he raised concerns about the price of energy and the speed of planning decisions.
"You cannot expect a US company to make a major investment here if they cannot be certain when they will get an answer from planning authorities," he told.
Mr Stephens, who was appointed ambassador by US President Donald Trump last year, was speaking at a Belfast Chamber dinner at Queen's University Belfast.
He said that Northern Ireland is a region that "punches above its weight".
But he added: "Now, I must temper my optimism with caution, because we do have concerns.
"As in the rest of the UK, energy prices here are too high to run an efficient and competitive industrialised economy.
"That is inhibiting US investment and harming both businesses and taxpayers.
"And while the United States is a longstanding friend of Northern Ireland and an advocate of its devolved government - your achievements in recent years have been nothing short of remarkable - for the Northern Ireland Executive to deliver a globally competitive economy, from pharma to critical minerals, approvals must be quicker.
"Bureaucracy must not become a barrier to progress," he said.
Mr Stephens drew attention to the Dalradian gold mine application.
The company, which is supported by US investment, wants to develop an underground gold, silver and copper mine on the Curraghinalt site near Greencastle, where it has been working for 15 years.
It said the proposed underground mine could create and support up to 1,000 jobs and add $5 billion (£4.1bn) to the Northern Ireland economy.
However, some opponents have raised concerns about the impact of the proposed mine on the environment and health.
A planning application was submitted in 2017 and a Planning Appeals Commission (PAC) inquiry was ordered by then infrastructure minister Nichola Mallon in 2020.
'We need a decision'
The probe opened for public hearings in Omagh earlier this year, but on the third day of evidence it was suspended.
"We need a decision on the Dalradian gold mine, fast," Mr Stephens said.
"It's been around eight years with no movement, and that is harming the region's reputation, while preventing potential jobs and investment here," he added.
"As the price of gold rises, this mine could bring valuable revenue to the local economy, helping Northern Ireland fund healthcare, education, and so much more.
"You are sitting on a literal goldmine, so please end this unnecessary delay."
Mr Stephens claimed it was a "symptom of a broader issue".
He added: "You cannot expect a US company to make a major investment here if they cannot be certain when they will get an answer from planning authorities.
"Those systems need to be predictable, and to move at the speed of business."
"Both President Trump and I are fierce advocates of the private sector, and of the special US-UK trade relationship," Mr Stephens said.
"We want the UK and Northern Ireland to succeed, because that makes us all stronger.
"It's why we put pen to paper on the Economic Prosperity Deal in May, and why US and UK firms signed over $350bn worth of cross-investment deals when President Trump came in September for his historic second state visit - including Bank of America's commitment to bring up to a thousand jobs to Northern Ireland.
"But we need our partners here to show the same faith and decisiveness, whether in planning decisions or in dealing with energy costs.
"Only then can we make our countries safer, stronger and more prosperous."
Earlier this month, Mr Stephens said US pharmaceutical companies will "shut down" their sites in the UK if the NHS does not pay more for drugs.
He also issued a rebuke after the Government announced the UK's first "small modular reactor" nuclear power station will be built at Wylfa, on Anglesey in north Wales.
Mr Stephens said the US was "extremely disappointed" by the decision.
He had been pushing for a larger reactor at Wylfa, and US firm Westinghouse had reportedly presented plans to the UK government to build a new gigawatt station at the site.
