U.N. Secretary-General Ban Ki-moon, left, escorted by Director of Acropolis Museum Dimitris Patermalis, looks at a 2,500-year-old Caryatid statue during his visit to the Acropolis Museum. (THE ASSOCIATED PRESS/Thanassis Stavrakis)

ATHENS - U.N. Secretary-General Ban Ki-moon is urging developed countries to slash greenhouse gas emissions by 25 to 40 per cent.

Ban described negotiations at next month's climate change summit in Copenhagen, Denmark as "complex." He says an agreement that is "comprehensive, equitable, balanced and binding" should be reached at the Dec. 7-18 talks.

Ban, who earlier cautioned that a legally binding deal may not be reached at the summit, spoke Thursday at Greece's parliament.

Key climate change negotiations are under way this week in Barcelona, Spain, ahead of the Copenhagen conference.