Environment ministers overcame seven years of obstacles today and committed to reducing the world's mercury pollution.

In a sign of America's return to a global leadership role, United Nations environment ministers meeting in Nairobi agreed to take immediate steps to limit exposure to mercury.

The White House said it would press hard for a legally binding treaty when negotiations get under way later this year.

"The United States will play a leading role in working with other nations to craft a global, legally binding agreement that will prevent the spread of mercury into the environment," said Nancy Sutley, chair of the White House council on environmental quality.

The Bush administration had blocked international efforts to limit mercury - although such protections are in place in America.

Mercury, which can travel thousands of miles from its original source, damages the central nervous system, and is especially dangerous to pregnant women and babies.

The treaty will include measures to reduce the supply of mercury and its use in products, such as thermomenters, and processes, like paper making. It will also seek to cut back on mercury emissions from coal-fired power plants, which are responsible for about half of the world's mercury pollution.

The new-found consensus in Nairobi, which saw the US, India and China lifting their resistance to a binding global mercury treaty, raised hopes for progress later this year at the crucial UN meeting in Copenhagen on an international climate change deal.

"There was a seismic shift from the American government from its previous position," said Nick Nuttall, the spokesman for the UN environment programme. "It was clear from the beginning of this week that the US negotiators had been given a clear line from Washington, and indeed the White House, to come together with the rest of the world and do something."

"The US has taken a leadership role that will chart a new course on mercury protections around the world. We have set a strong example that is already influencing others to do the same," said Susan Egan Keane, an analyst at the US National Resources Defence Council.

Barack Obama had earlier taken a number of steps at home to break with the George Bush legacy on the environment - most notably restoring the power of government agencies to regulate carbon dioxide from power plants.

The strong push from the US side in Nairobi this week evidently helped wear down resistance from governments such as China and India. China is heavily dependent on coal-fired power plants, while Indian manufacturers still use many processes that depend on the metal.

The eight-point plan agreed on Friday calls for reduction in mercury emissions from power plants, and in its use in thermometers and other household products, as well as in plastics production and paper-making. It would cut down on the use of mercury in gold panning, a process that results in huge quantities of the heavy metal being washed into streams.

Mercury is a naturally occurring element, but pollution has caused levels to rise sharply in many fish species, increasing the danger to humans that eat them.

"Today the world's environment ministers, armed with the full facts and full choices, decided the time for talking was over - the time for action on this pollution is now," said Unep's director, Achim Steiner.

Formal treaty negotiations will get underway later this year, with a view to reaching a final agreement in 2013.