A UN conference aimed at reducing greenhouse gases has begun in the Italian city of Milan, with participants hoping to agree on the details of the 1997 Kyoto Protocol.

The ninth Conference of the Parties to the UN Framework Convention on Climate Change will continue until December 11, and is expected to attract about 4,000 delegates.

The protocol requires industrialised countries to slash their greenhouse gas emissions from 1990 levels by an average of 5.2 per cent between 2008 and 2012.

Russia is seen as holding the key to the future of the protocol, because it will enter into force 90 days after Moscow's ratification.

The US, the biggest single polluter, withdrew from the pact two years ago, but both countries will be represented at the conference.