VIENNA -- The chief UN arms inspector Hans Blix said Friday Iraq appeared to be making fresh efforts to cooperate with UN teams hunting banned weapons, as Washington said the "momentum is building" for war with Iraq, Reuters said.

Iraq said UN inspectors Thursday held their first private interview with an Iraqi scientist linked to previous banned weapons programs, a key UN demand.

Blix welcomed the move but said he wanted to see "a lot more" during his weekend visit to Iraq. "We want to see disarmament of Iraq through the inspection process," he said in a speech to new weapons inspectors being sent to Iraq. "It requires active cooperation from Iraq, not on process but on substance."

Weapons inspectors have demanded that experts be interviewed without other Iraqis present, to protect informers from reprisal. To date, Iraq has refused to allow U2 spyplanes to overfly its territory to monitor suspected sites, which Secretary of State Colin Powell said this week were being doctored by the Iraqis to hide banned weapons programs.

Blix and Mohamed Elbaradei, head of the UN's atomic watchdog agency, the IAEA, travel to Baghdad this weekend for talks with Iraqi leaders seen by many as President Saddam Hussein's last chance to avert war.

They are to report to the UN Security Council on February 14. A critical report could increase pressure for a new UN resolution to authorize war.

President Bush said Thursday he would support a new UN resolution authorizing war against Iraq, saying "the game is over" for Saddam and challenging the Security Council to stand up to Iraq's defiance.

"Having made its demands, the Security Council must not back down, when those demands are defied and mocked by a dictator," Bush said.

Iraq denies it has any weapons of mass destruction and on Thursday poured scorn on U.S. charges it was cheating inspectors or had links with Al-Qaeda, blamed for the September 11, 2001 attacks on U.S. cities.

Iraqi officials responded angrily to Powell, who on Wednesday presented the Security Council with spy satellite photos, tapes of bugged conversations and other material he said was damning evidence of Iraq's determination to hide weapons.

Saddam adviser Amir al-Saadi said the allegations were "outrageous and not convincing," and would be rebutted line by line in a detailed letter to the Security Council.