The German pope also called for the dismantling of nuclear weapons and an effective demilitarisation around the world, expressing concern that more countries seem to want to acquire nuclear weapons.

His message, "The Human Family, A Community of Peace," also spelled out the Roman Catholic Church's opposition to gay marriage, saying that any weakening of the traditional family was "an objective obstacle on the road to peace."

The Roman Catholic Church marks World Peace Day on January 1 and the Pope's written message is traditionally sent to heads of government and international organisations.

The environment took up much of the message and although its release coincided with the U.N. climate talks in Bali, aimed at launching talks on a global pact to succeed the 1997 Kyoto Protocol, the Pope did not mention them.

"Humanity today is rightly concerned about the ecological balance of tomorrow," he said. But environmental assessments must be "carried out prudently" and "uninhibited by ideological pressure to draw hasty conclusions."

Efforts to protect the environment should seek "agreement on a model of sustainable development capable of ensuring the well-being of all while respecting environmental balances."

"Prudence does not mean failing to accept responsibilities and postponing decisions," but a commitment to making joint rather than unilateral decisions, he added.

The Pope dedicated another section of the message to nuclear issues and called for disarmament. "Humanity today is unfortunately experiencing great division and sharp conflicts which cast dark shadows on its future," he said, lamenting that more countries wanted to possess nuclear weapons.

He called for "an effective demilitarisation" around the world, saying too many developing nations were locked in an arms race and were allotting scant resources to weapons.

Nuclear non-proliferation appeared to be at a standstill, he said. "I feel bound to entreat those in authority to resume with greater determination negotiations for a progressive and mutually agreed dismantling of existing nuclear weapons."