To their users, bike hire networks like that just launched in London and the popular Vélib scheme in Paris might seem no more than a convenient, fun way to get around a city. But they're wrong.

Dan Maes, the Republican frontrunner to challenge for Colorado's governorship has discovered the truth about such cycle schemes: they are a grand United Nations plot to enslave the US.

"This is all very well disguised, but it will be exposed," Maes told supporters at a campaign rally.

"This is bigger than it looks like on the surface, and it could threaten our personal freedoms. These aren't just warm fuzzy ideas from the mayor. These are very specific strategies that are dictated to us by this United Nations programme that mayors have signed on to."

His target is a programme called the B-Cycle in Colorado's capital, Denver, a planned network of 400 red bikes to be placed at docking stations around the city and accessible using swipe cards. B-Cycle already operates in Chicago and hopes to expand to other US urban areas.

Maes argues that Denver's bike scheme, and other policies promoted by the city's Democratic mayor, John Hickenlooper, such as encouraging employers to install showers for cyclists, are the brainchild of the International Council for Local Environmental Initiatives (ICLEI), a UN-linked organisation connecting 1,200 communities worldwide.

If the Tea Party-endorsed Maes wins the Republican nomination he will face Hickenlooper in the election to be governor.

Maes conceded that some might find his theory "kooky". He explained: "At first I thought: 'Gosh, public transportation, what's wrong with that, and what's wrong with people parking their cars and riding their bikes? And what's wrong with incentives for green cars?' But if you do your homework and research, you realize ICLEI is part of a greater strategy to rein in American cities under a United Nations treaty."

A spokesman for Hickenlooper said Denver joined the ICLEI in 1992, more than a decade before he became mayor, and had "limited" contact with the organisation.