US investment events for Belfast and Derry have been postponed because of Brexit, Deputy First Minister Martin McGuinness has said.
Business executives had planned to visit in October but they have now been delayed until next year.
The delegates would have included executives from cyber-security and bio-medical sciences potentially looking to use the north to expand their operations.
Mr McGuinness said he was concerned it was becoming more difficult for the north to attract foreign investment following the EU referendum.
"Plans were in place for an economic mission of considerable size for October of this year and that was on the basis they hoped the vote on Brexit would be a remain vote," the Sinn Fein MLA said.
"Now since that is not the case I have been told yesterday at a meeting that that visit has now been postponed, directly as a result of the vote.
"That is of considerable concern."
A US Consulate spokesman in Belfast said: "We are strongly committed to bolstering two-way trade and investment with Northern Ireland.
"We anticipate that a US trade and investment delegation will visit Northern Ireland in the first half of 2017."
Meanwhile, the Northern Ireland Chamber of Commerce has said businesses need clarity around the implications of Brexit,
Although its members hold different views on last month's EU referendum result, president Nick Coburn said they all needed to know basic facts about the implications of the vote.
"Following a brief period of reflection, businesses want to understand when changes will occur in government, when Article 50 will be triggered, and what the time-frame for negotiation will be thereafter," he said.
The organisation called for stability for markets and business confidence, clarity on the timings for Brexit decisions and action to support the economy at a sensitive time of transition.
Mr Coburn said business people also wanted to see the Executive progress the north-south power interconnector, reform rates and provide access to money raised from a proposed apprenticeships' levy.
He was speaking as the Ulster Farmers’ Union drew up its list of priorities before the process for negotiating a replacement for the EU's common agricultural policy begins.
President Barclay Bell said it included maintaining support to farmers equivalent to that provided by the EU, maintaining access to seasonal and full time labour and minimising disruption to existing trade relationships between the north and Republic.
Politicians also held another series of meetings about the implications of Brexit yesterday.
Finance Minister Máirtín Ó Muilleoir and the Republic's Minister for Public Expenditure Paschal Donohoe discussed how funding could continue for the EU's Peace and Interreg programmes in Ireland.
"It is very clear there is €500m in the balance and myself and junior minister Alastair Ross and Minister Donohoe want to secure that money," Mr Ó Muilleoir said.
SDLP representatives, including assembly members Alex Attwood and Claire Hanna, also met US Senator Gary Hart in Belfast yesterday morning to seek his help in lobbying Ireland's case.
