BAGHDAD, Iraq -- Iraq denied reports it is trying to collect material for nuclear weapons and building up sites once targeted by U.N. inspectors, saying Sunday the claims were lies spread by the United States and Britain to justify an attack.

The denial came as President Bush has begun taking his case for possible military action against Iraq to his allies, meeting the day before with British Prime Minister Blair at Camp David and preparing to deliver a key speech at the United Nations this week.

Blair -- the strongest voice in support of Bush amid much European criticism -- said Sunday he believed that those opposed to action would change their minds after seeing evidence of the threat that Iraqi leader Saddam Hussein allegedly poses.

Blair told Sky news television that critics are asking "sensible questions," but said they "can be convinced if they see the evidence."

Iraqi Vice President Taha Yassin Ramadan dismissed reports from recent days cited as evidence against Saddam's government.

The head of a U.N. atomic weapons team said Friday that satellite photos show new construction at several sites linked to Saddam's past nuclear efforts. And a U.S. intelligence official said that Iraq has recently stepped up attempts to import industrial equipment that could be used to enrich uranium for use in nuclear weapons.

'Telling lies'

"There is no such a thing," Ramadan told reporters when asked about both reports. "They are telling lies and lies to make others believe them."

He said the United States and Britain were seeking an excuse to attack Iraq.

In the United States on Sunday, Vice President Dick Cheney said Saddam is "actively and aggressively" trying to build a nuclear bomb and argued that the United States is justified in striking first against any government that plans to attack America.

Blair said Sunday that the United States and Britain would rally "the broadest possible international support" for stopping Saddam from stocking biological and chemical weapons or acquiring nuclear arms.

France, Germany, Russia and China have all been outspoken opponents of any unilateral U.S. attack on Baghdad.

Moscow said Sunday that such an attack would cause disorder in the Middle East and undermine international anti-terrorism efforts.

"If, under the pretext of combatting terrorism, attempts are made to interfere in the internal affairs of sovereign states, it will ... inflict irreparable damage on unity within the anti-terror coalition," Igor Ivanov said, according to the Interfax news agency.

Iraq has come under pressure from Europe and Arab nations to accept U.N. weapons inspectors in hopes of defusing the crisis.

Scott Ritter, an American who was once on the inspections teams, visited Baghdad on Sunday, saying Iraq posed no threat and urging it to prove that by opening up to inspections.

Cooperation on inspectors would leave the United States "standing alone in regards to war threats on Iraq and this is the best way to prevent the war," Ritter said on his third visit arranged by the Iraqi government since he resigned from the U.N. inspection team in 1998.

Secretary of State Colin Powell said Ritter was no longer "in the intelligence chain."

Other members of the U.N. teams that investigated Iraq's weapons of mass destruction from 1991 to 1998 have told The Associated Press that Iraq probably possesses large stockpiles of nerve agents, mustard gas and anthrax.

They add that while the country does not have a nuclear bomb, it has the designs, equipment and expertise to build one quickly if it were able to get enough weapons-grade uranium or plutonium.

Many former inspectors say Iraq's arsenal is not much of a threat because Saddam has been deterred so far by fear of U.S. retaliation and apparently has been reluctant to share his weapons with terrorists.

Iraq, while denying it still has weapons of mass destruction, has offered only to continue dialogue with the United Nations about the return of inspectors. It has not responded to U.N. Secretary-General Kofi Annan's demand that inspectors be allowed to return unconditionally as a first step to further talks.

"We want to maintain dialogue only with the United Nations without the pressuring of a certain country," said Ramadan, the Iraqi vice president. "If the United States attacks Iraq not only Arabs but the whole world will oppose it, if they have one enemy today then there will be 10 more."

Sanctions imposed on Iraq for its 1990 invasion of neighboring Kuwait cannot be lifted until U.N. inspectors certify that the country has surrendered nuclear, chemical and biological weapons and the missiles to deliver them.