U.N. atomic agency inspectors will visit any site considered necessary to check Iran's claims that it doesn't want to make nuclear weapons, the agency chief said Thursday after arriving in Tehran for key talks.

International Atomic Energy Agency (search) chief Mohamed ElBaradei (search) traveled to Iran to warn that an Oct. 31 deadline leaves the government little time to prove its claims.

Two weeks ahead of the ultimatum -- and the subsequent threat of possible U.N. Security Council sanctions -- there are "still outstanding issues to be resolved" before suspicions are dispelled, ElBaradei told The Associated Press after landing.

ElBaradei said it wasn't too late for Iran to assist U.N. nuclear inspectors. He would not give details of ongoing inspections, but suggested reviews of both military and civilian facilities.

"If it's civilian or military sites doesn't matter much," he said. "We visit sites that are relevant to our work. If it's important to us to visit a site, we will do so."

The United States and its allies accuse Iran of working on a secret nuclear weapons program, while Tehran says it is only interested in generating electricity.

Earlier, while flying to Frankfurt from Vienna for a connecting flight to Tehran, ElBaradei told AP that despite the outstanding questions, Tehran had increased cooperation with agency officials in recent weeks, permitting inspectors visits to all sites they requested, including a military one.

"We asked and we were allowed to go there," ElBaradei said.

Officials close to the agency, speaking on condition of anonymity, identified that site as Kolahdouz, not far from the Iranian capital.

The site was identified in the summer by the National Council of Resistance of Iran (search) as the alleged location of efforts to enrich uranium. They said centrifuge equipment there was reputedly meant to operate as a supplement to the uranium enrichment site, in Natanz.

IAEA experts have a list of several other military sites they hope to visit, the officials confirmed. ElBaradei said he would not comment on his Iran probe before presenting his report to the next board meeting. The board convenes again on Nov. 20.

"I think we need all the information that we requested, and so far we have not received all this information," ElBaradei said. "The key issue is the enrichment program -- to make sure we have seen all nuclear experiments that have taken place in Iran, that we have seen all the nuclear material in Iran."

If the agency's board of governors finds next month that Iran has not answered all questions about its nuclear program by Oct. 31, they could refer the issue referred to the U.N. Security Council for possible sanctions.

Iran twice has confirmed in recent months that particles of weapons-grade enriched uranium were found in separate places in the country. But the government maintains its equipment was "contaminated" by a previous owner.

Iran has signed the Nuclear Nonproliferation Treaty, which bans the spread of nuclear weapons.

Ali Akbar Salehi, Iran's senior delegate to the IAEA, said earlier this month that Tehran and agency representatives reached "total agreement" on measures to prove the country's nuclear program is peaceful. For example, Iran will provide the IAEA with a list of the imported equipment it contends had been contaminated.

But ElBaradei suggested there was some foot-dragging.

"There has been increased cooperation, but again there are a lot of outstanding important issues that remain ... we don't have much time left," he said.

Diplomats said documentation was still lacking on the origin of the centrifuge parts Iraq said it imported. Without that, the agency cannot compare isotope traces to establish whether the contamination came from abroad, as Iran asserts.

"We are getting lists, but we still need to be receiving more information as to the origin of this equipment," ElBaradei said.

ElBaradei he was going to Tehran on request of the country's leaders.

"It was their view that my visit there will move things forward," he said.