Inspectors also visited private homes for the first time Thursday, as the chief U.N. inspector described the situation in Iraq as "very tense and very dangerous."
A team from the U.N. Monitoring, Verification and Inspection Commission (UNMOVIC) made the warhead discovery at the Ukhaider ammunition storage area, where they went to inspect a large group of bunkers constructed in the late 1990s.
The inspectors found 11 empty 122 mm chemical warheads and one warhead that requires further evaluation. The warheads are similar to ones imported by Iraq during the late 1980s, the spokesman said.
The UNMOVIC team used portable X-ray equipment to analyze one of the warheads and collected samples for chemical testing.
Earlier, U.N. team searched homes owned by Iraqi scientists in the hunt for evidence of weapons of mass destruction, Iraqi officials said.
The homes are located in the Al-Ghazaliyah district in Baghdad and are not listed as declared sites by Iraq, suggesting that inspectors may have been working on an intelligence tip.
Blix: Iraq violated import ban
After meeting with European Union officials in Brussels, Belgium, chief U.N. inspector Hans Blix told reporters Iraq has illegally imported arms-related material as recently as 2002, but it is not yet clear whether the material is related to weapons of mass destruction.
"It's clear they have violated the bans of the United Nations in terms of imports," Blix said. The imported items include missile parts, CNN's Richard Roth reported.
U.S. officials reacted positively to Blix's comments.
"The evidence is mounting, and while inspectors went in with a stiff upper lip it is now more clear by the day that things are not going nearly as well as the public has been led to believe," one official said.
President Bush, in a speech Thursday in Scranton, Pennsylvania, repeated his warning that time is running out for Saddam Hussein to comply with demands to disarm.
"So far the evidence hasn't been very good that he is disarming. And time is running out." Bush said. "At some point in time the United States' patience will run out."
"We try our best to make the inspections effective," Blix said, "so that we can have a peaceful solution." But, he warned, "the other major option, as you know, is the one we've seen taking shape in the form of an armed action against Iraq."
Diplomats: Iraq must be 'proactive'
Blix and Mohamed ElBaradei, director general of the International Atomic Energy Agency, are due to visit Iraq next week ahead of their report to the U.N. Security Council on January 27. Blix has said he plans to tell Iraq to submit new weapons evidence.
After the talks in Brussels with Blix, the EU's foreign policy chief Javier Solana expressed his solidarity with the chief weapons inspector.
Solana told reporters: "He (Blix) has conveyed to me his concern that the cooperation with Saddam Hussein, the cooperation with Iraq, is not sufficient.
"We are demanding a more proactive cooperation from the regime of Saddam Hussein so that the world, the Security Council, the inspectors, are convinced that he has disarmed from all weapons of mass destruction."
ElBaradei, speaking after two days of talks with Russian officials, also used the term "proactive" to describe what is required of Iraq.
"What they ought to do is come forward" provide documents or physical evidence to support the conclusion that the country no longer has weapons of mass destruction, he said.
"This kind of proactive approach is not there. And that's why I said they need to shift gears," ElBaradei said. "As long as we can continue to go around the country and come to the conclusion, 'well we are not 100 percent sure,' this is not good enough for the Security Council."
There remains a dispute over a timetable for the inspections.
The White House wants the January 27 report from Blix and ElBaradei to be a major threshold for deciding whether Iraq is complying with the U.N. demands. Blix has cited previous U.N. resolutions and said he will report to the Security Council again in March.
A senior White House official said Thursday that, "in a climate of delays, resistance and obstruction we don't see the value" in indefinitely extending the work of the inspectors.
In another development, sources said that during a meeting Tuesday, U.S. National Security Adviser Condoleezza Rice pressed Blix and other senior U.N. officials to demand that Iraq allow certain scientists and their families to travel outside the country for interviews about weapons of mass destruction programs.
The move would reflect a more muscular interpretation of U.N. Security Council resolution 1441, which said that inspectors "may at their discretion conduct interviews inside or outside of Iraq, (and) may facilitate the travel of those interviewed and family members outside of Iraq."
To date, U.N. weapons inspectors have only asked Iraqi scientists whether they would be willing to be interviewed outside of the country, or interviewed without the presence of Iraqi government representatives. None have agreed so far, U.N. officials said.