Vatican City — Pope John Paul issued his strongest criticism yet of a possible war with Iraq, saying Monday that military force can only be used as "the very last option" — and then only under certain conditions.

Amid a buildup of U.S. forces in the Persian Gulf, the Pope urged political leaders to step up their diplomatic efforts to avoid war, which he said would only harm ordinary Iraqis "already sorely tried" by 12 years of UN sanctions.

"War is not always inevitable. It is always a defeat for humanity," the Pope told Vatican-based diplomats in his annual speech on issues of concern to the Roman Catholic Church.

"As the charter of the United Nations organization and international law itself remind us, war cannot be decided upon, even when it is a matter of ensuring the common good, except as the very last option and in accordance with very strict conditions, without ignoring the consequences for the civilian population both during and after the military operations."

It was the Pope's strongest message yet in opposition to war, and it was the first time since the crisis erupted that he has publicly mentioned Iraq by name.

Previously, the Pope has only referred in general to the threats of war and, in his Christmas message, called on the world to "extinguish the ominous smoldering of a conflict."

Other Vatican officials have been more explicit, saying in recent newspaper interviews that a "preventive war" against Baghdad would have no moral or legal justification, and would only create antagonisms between Christians and Muslims.

The U.S. ambassador to the Holy See, James Nicholson, said the United States agreed with the pope's comment that war isn't always inevitable.

"President Bush has said war is a last resort," Mr. Nicholson said after the speech. "War won't be necessary" if Iraqi President Saddam Hussein abides by UN resolutions and gets rid of his weapons of mass destruction, he said.

Pope John Paul was a strong opponent of the 1991 Gulf War and has frequently spoken out about the plight of Iraqis suffering under sanctions imposed after Baghdad invaded Kuwait in 1990.

In his speech, the Pope also touched on other issues of concern to the church, including the "crisis" in Vatican-Russian relations and what he called the risks to the dignity of human life: abortion, euthanasia and human cloning.

The three, he said, "risk reducing the human person to a mere object: life and death to order, as it were!"

"When all moral criteria are removed, scientific research involving the sources of life becomes a denial of the being and the dignity of the person," he told the diplomats gathered in the frescoed Sala Regia of the Vatican's Apostolic Palace.

The Pope has long voiced opposition to abortion and euthanasia, and the Vatican has recently entered the debate of cloning and research using stem cells from human embryos.

Vatican spokesman Joaquin Navarro-Valls, for example, called the recent claims that a cloned baby had been born "an expression of a brutal mentality, devoid of any ethical and human consideration."

On Russia, the pope denounced the expulsion of five foreign-born Roman Catholic priests and said he expected Russia to "end to the crisis."

"Russian Catholics wish to live as their brethren do in the rest of the world, enjoying the same freedom and the same dignity," he told the diplomats.

He stressed that dialogue between Christians and with other religious "in particular with Islam, are the best remedy for sectarian rifts, fanaticism or religious terrorism."