President Bush and Russian President Vladimir Putin (search) urged North Korea and Iran on Sunday to halt development of nuclear weapons, and Bush stood by his assertion that Iraq possessed weapons of mass destruction.

Both the United States and Russia are "determined to meet the threats of weapons of mass destruction," Bush said at a joint news conference. "We strongly urge North Korea to visibly, verifiably and irreversibly dismantle its nuclear program."

He added: "We are concerned about Iran's advanced nuclear program and urge Iran to comply in full with its obligations under the Nuclear Non-Proliferation Treaty (search)."

While agreeing that they both oppose the spread of nuclear technology, the two leaders remained at least partly at odds over Iran's nuclear program.

The Bush administration claims Russian sales of technology to Iran is helping Tehran to develop a nuclear weapons program. Russia has denied that its help is going toward weapons development; Iran says its nuclear program is strictly for peaceful development of energy.

"Russia and the United States have mutual concerns about the advanced Iranian nuclear program. We understand the consequences of Iran having a nuclear weapon and therefore we want to work together ... to make sure they do not have a nuclear weapon," Bush said. "I appreciate Vladimir Putin's understanding of the issue, and his willingness to work with me and others to resolve this."

But Putin, while agreeing that the spread of nuclear weapons should be prevented "not just in Iran but in other regions," had some pointed words on the subject.

"We are against using the pretext of a nuclear weapons program (in Iran) as an instrument of unfair competition against us," he said. "The position of Russia and the United States on the issue are much closer than they seem.We need no convincing about the fact that weapons of mass destruction proliferation should be checked and prevented throughout the world."

Bush answered tersely when asked about the search for weapons of mass destruction in Iraq. Bush charged that Iraq had such weapons, and used the allegation as his primary justification for going to war there.

"We've discovered weapons systems, biological labs, that Iraq denied she had, and labs that were prohibited under the U.N. resolutions," Bush said.

Earlier this weekend, Bush pointed to two suspected biological laboratories found in Iraq. But both the Pentagon and U.S. weapons hunters have said the labs do not constitute arms. U.S. intelligence concluded last week that the mobile labs probably were designed to produce biological weapons.

Putin offered no opinion on whether such weapons will be found in Iraq. Prime Minister Tony Blair, in an interview with Sky News Television, said he had "no doubt whatever that the evidence of Iraqi weapons of mass destruction will be there. Absolutely."

Russia opposed the U.S. invasion of Iraq, leading to friction with the United States, but both leaders said they were putting the dispute behind them.

The "fundamentals of the relations between the United States and Russia turned out to be stronger than the forces and events that tested it," Putin said. Bush nodded in agreement, and said terrorism will unite the two countries.

"We are working closely to confront the challenges of our time," Bush said. "Both of our countries have suffered greatly at the hands of terrorists, and our governments are taking action to confront this threat."

Bush invited Putin to Camp David in September, and Putin seemed to signal with a nod that he accepted. The two leaders held their news conference while seated at massive twin white desks inside Konstantin Palace in St. Petersburg, Putin's hometown. They met privately for 45 minutes before the news conference.

The two leaders signed papers certifying both Russia and the United States have now formally ratified the "Treaty of Moscow," the agreement last year to reduce arsenals on both sides by two-thirds. The U.S. Senate passed it earlier this year, and the Russian parliament ratified it last month.

Russia has a long history of involvement with Iraq's oil sector, and Putin made clear his country would prefer to carve out a role for its companies in Iraq's future. He offered "all our expertise, experience and resources" to that end.

Bush acknowledged Russia's experience and history, but made clear that "the Iraqi people will make the decision that is in their best interests" concerning Iraq's oil industry.

Bush's remarks Sunday, and a speech Saturday in Krakow, Poland, set a conciliatory tone for the Group of Eight (search) meeting, an annual summit of major industrialized nations in Evian, France. Differences over Iraq caused an unprecedented breach between the United States and longtime partners such as France and Germany, which led the opposition to the war. With prompting from Washington, some Americans have refused to buy French products.

Bush spoke to German Chancellor Gerhard Schroeder for the first time in six months on Sunday.

"How are you?" Bush said after approaching Schroeder in St. Petersburg and offering his hand, according to German officials. The two leaders spoke briefly but were not seated at the same table during a banquet dinner. They had not spoken since November when Schroeder ran for re-election on an anti-war platform.

The G-8 meeting runs through Tuesday, but Bush will cut short his stay and depart for the Middle East on Monday for talks with Arab leaders in Egypt and then a summit in Jordan with Israeli Prime Minister Ariel Sharon and Mahmoud Abbas, the new Palestinian prime minister.