The statement contrasts with earlier media reports saying China will introduce a tax before 2015 and underscores global interest in how China plans to address climate change in the years ahead.

China emitted a quarter of mankind's greenhouse gas pollution in 2010 and emissions are expected to keep rising in line with growing energy demand.

Speaking at the World Resources Institute in Washington, Su Wei, China's chief negotiator on climate change, said a tax on carbon was one of several policy options for China to reduce its greenhouse gas emissions, the highest of any nation.

But China plans to launch a carbon trading scheme, and adding a tax on major emitters could complicate legislation.

"There may be some overlap between the two systems. Of course, the two systems are not mutually exclusive. We need to have a very careful consideration," Su told reporters at WRI, an international think tank.

A decision on a carbon tax would be delayed until there was clarity on whether and how the two instruments could co-exist.

Chinese state media reported last week that a government-affiliated think-tank, the Financial Science Research Institute, had proposed to the Ministry of Finance that China implement a 10 yuan ($1.58) per tonne tax on emissions from big energy users before 2015.

That report stirred debate in Australia, which will launch a national carbon pricing scheme from July this year set at an initial A$23 ($23.70) a tonne for the top 500 polluters. Some opponents said Australia's much higher starting price for the tax would hurt the global resource exporter's competitiveness.

However, Fu Zhihua, a researcher at the institute denied the reports this week, saying a carbon tax is not yet on the agenda of lawmakers at the ministry.

The National Development and Reform Commission (NDRC), where Su Wei is director general of the climate change department, has the main responsibility for carbon policies in China.

The NDRC has picked seven cities and provinces to launch pilot emissions trading schemes from 2013, and aims to launch a nationwide CO2 market later in the decade.

But in parallel, major emission sources such as coal and natural gas could become subject to regulations by the Ministry of Environmental Protection, which is designing an environment tax.

Chinese think-tanks have been studying carbon taxation for several years, but so far there has been little coordination between them.

Speaking in Washington, Su Wei also noted that China already had a high taxation level, and in the current difficult economic climate the government would be careful to launch new taxes.

Su led a delegation of officials from five Chinese cities on a trip to the United States to learn about low-carbon sustainable development.

Among others, the delegation met with officials from the Regional Greenhouse Gas Initiative (RGGI), a north-eastern U.S. carbon scheme covering nine states, California and the Western Climate Initiative.