The European Commission on Wednesday said the EU will link its carbon trading market to the United Nations' scheme by December at the latest.

The joined-up schemes should give Europe's biggest polluters -- such as the steel, construction and energy firms -- more leeway to subsidise CO2 reduction projections worldwide in return for credits in the EU's trading system.

The linking of the two systems will enable companies to transfer so-called "certified emission reductions" (CERs) issued under the UN's Clean Development Mechanism to EU member states.

The commission said in a statement that the two registers would be linked "before December 2008 at the latest".

The EU and the UN have carried out two rehearsals to test technical procedures.

The first test-run, which took place in May, involved five member states. The second, which ended on Monday, involved all member states, as well as registries in Russia, Japan and New Zealand.

"These tests have now been successfully completed," the commission said.

"I welcome the successful outcome of the testing phase," EU Environment Commissioner Stavros Dimas said.

"Linking up with the UN's carbon credit registry will further strengthen Europe's leading role in the global carbon market," linking it to non-European countries such as Australia and Japan.

The EU's register, which has been operational since 2005, is the central registry for tracking ownership of allowances in the EU Emissions Trading System.

The International Transaction Log (ITL) keeps track of various types of UN credits from countries that have signed up to the Kyoto Protocol.

After the hook-up, the two systems will control and track transactions jointly.

"We are negotiating with the United Nations... to decide the (exact) date," a European Commission spokeswoman said.

The EU has fixed emission quotas for each of the 27 member states in a bid to cut down on greenhouses gases and tackle climate change.

Overall the European Union is seeking to cut carbon emissions by 20 percent by 2020.

Brussels want industry to pay for the right to pollute by 2013.

These rights could be traded with a ton of CO2 currently put at around 30 euros, a two-year high.