U.N. arms inspectors may start inviting Iraqi scientists suspected of being linked to weapons programs for private interviews this week, a step Washington sees as key to uncovering Saddam Hussein's weapons of mass destruction, a U.N. spokesman said Saturday.

The inspectors visited more suspected weapons sites Saturday, a day after the United States ordered 35,000 additional troops to the Gulf in a move that appeared to bring closer the prospect of an American invasion of Iraq.

U.N. spokesman Hiro Ueki said a team of missiles experts revisited the Ibn Sina military complex at Tarmiya, 25 miles north of Baghdad, a site in which Iraqi scientists in the 1980s had tried to enrich uranium to a level suitable for atomic bombs.

Ueki said Saturday's visit was aimed at checking equipment and materials used in chemical processes linked to missile activities.

Another team flew by helicopter to an area 188 miles northwest of Baghdad to inspect an airfield. It was only the second time since six U.N. helicopters became operational Jan. 7 that they have been used. Bad weather prevented earlier flights.

Other sites visited Saturday included five colleges in a provincial university, two branches of a state pharmaceutical company, a dairy plant in the northern city of Mosul and a plant south of Baghdad that produces explosives for military and civilian purposes.

Ueki said U.N. Monitoring, Verification and Inspection experts may be ready to begin asking Baghdad this week to let them privately interview Iraqi scientists after they finish studying Iraq's 12,000-page weapons declaration and a list of names of experts involved in arms programs.

"These things take time," Ueki told The Associated Press in Baghdad, adding that he had no details if or when U.N. experts would ask to take Iraqi scientists abroad for interviews.

Last month, inspectors from the International Atomic Energy Agency interviewed two Iraqi scientists, who requested that Iraqi minders be present during the meetings.

Mohamed ElBaradei, the head of the U.N. nuclear agency, has complained that inspectors haven't been able to talk to scientists without Iraqi officials being present.

"We are not able to have interviews in Iraq in private and that does not show the proactive cooperation we seek," ElBaradei said Thursday after briefing the U.N. Security Council on the progress of inspections and assessments of Iraq's weapons declaration.

Iraq is unlikely to refuse fresh requests for private interviews with its scientists but has indicated it could be less than keen on its scientists going abroad for interviews.

On Friday, U.S. Defense Secretary Donald H. Rumsfeld signed an order for 35,000 troops to head toward the Gulf, the single largest deployment order since the U.S. military buildup began last month. The troops will leave for the region in stages this month.

With these troops and the roughly 60,000 military personnel already in the region, America has almost reached its goal of 100,000 troops in the potential war zone by Jan. 31.

Britain's aircraft carrier HMS Ark Royal also set sail Saturday toward the Gulf at the head of the biggest British naval task force assembled in two decades. It is heading for a long-planned exercise in southeast Asia, but its course will take it to the Gulf, where it could be used in any military attack on Iraq.

Iraq remained defiant in the face of the military buildup.

"Iraq is ready for all probabilities and will fight as it should if attacked," Deputy Prime Minister Tariq Aziz said Saturday during a visit to Algeria.

"If the aggression can be avoided, fine, but not on the basis of surrendering to blackmail and threats," the official Iraqi News Agency quoted him as saying.

U.S. officials said the Pentagon has been sending e-mails to Iraqi officers warning them against following orders from Saddam to use chemical or germ weapons against U.S. or allied forces.

Weapons inspections resumed Nov. 27 under a toughened U.N. resolution that let inspectors interview Iraqi scientists in private or even abroad, in a bid to encourage them to expose hidden programs. The inspectors want to determine if Iraq still holds weapons of mass destruction in violation of U.N. resolutions.

Iraq denies it possesses such weapons, but America and Britain insist it does and have threatened to disarm Iraq by force.

Before leaving to Saudi Arabia on Saturday, Turkish Prime Minister Abdullah Gul urged Saddam to comply with inspections and avoid war, saying it could threaten regional stability.

Turkey, a NATO ally, has agreed to let America inspect its ports and air bases for possible use in an Iraq conflict. But it is under public pressure at home to not support a new Gulf war.

In Kuwait, Deputy Prime Minister Sheik Sabah Al Ahmed Al Sabah said he hoped Iraqis topple Saddam to prevent war. Kuwait has not before officially raised its desire for a coup in Baghdad.