President Bush called the idea of Tehran possessing a nuclear weapon "unacceptable" following reports Friday that scientists in Iran had succeeded in doubling the country's uranium enrichment.
"Whether they doubled it or not, the idea of Iran having a nuclear weapon is unacceptable," Bush told reporters in brief comments following a meeting with NATO Secretary-General Jaap de Hoop Scheffer in the Oval Office.
Bush said he knew about "speculation" that Iran has started enriching uranium.
"It says to me that we must double our effort to work with the international community to persuade the Iranians that there is only isolation from the world if they continue working forward on such a program," Bush said.
Bush's comments came after reports emerged that Iran succeeded in injecting gas into a second network of centrifuges, according to the Iranian Students News Agency. The agency quoted an anonymous official that confirmed that Iran is getting good results from enrichment tests.
World leaders are considering a draft resolution in the U.N. Security Council that would impose some sanctions on Iran after the country has refused to halt uranium enrichment.
The United States and European allies support a draft resolution that would ban the sale of missile and nuclear technology to Iran. It also would cut off some assistance from the International Atomic Energy Agency. Some reports show that China and Russia want to continue negotiations instead of issue sanctions.
The ISNA quoted an anonymous official confirming that Iran is injected gas into the second cascade.
"We are injecting gas into the second cascade, which we installed two weeks ago," ISNA quoted the anonymous official as saying.
The source of the report is questionable though since Iranian officials might leak information to ISNA to get it published instead of notifying official media.
Iran's uranium enrichment expansion should not cause problems with negotiations, Ali Larijani, Iran's top nuclear negotiator told ISNA in a separate story.
"It is possible to review both nuclear and regional issues through negotiation," Larijani was quoted as saying.
Larijani dismissed that Iran's nuclear program is wrong, saying it is only for civilian use such as generating electricity.
"Negotiations should be held in a rational and free climate," Larijani said. "We cannot attend conditional talks."
The Iran official quoted by ISNA said the nuclear watchdog was fully aware that Tehran was injecting the gas in its new centrifuges, and that nuclear inspectors had already arrived in Iran.
Diplomats at the IAEA would not comment Friday on whether inspectors had yet arrived in Iran.
The Islamic Republic first produced a small batch of enriched uranium in February from a cascade of 164 centrifuges at its nuclear plant at Natanz, central Iran. Iran says it plans to install 3,000 centrifuges at Natanz by the end of this year. Some 54,000 centrifuges would be required to produce enough nuclear fuel for a reactor.
Although Iran is nowhere near that goal, its successful operation of more cascades of centrifuges indicates that the country is gradually mastering the complexities of producing enriched uranium.
Iranian President Mahmoud Ahmadinejad said earlier this week that his country's nuclear capability had increased tenfold despite Western pressure to curb its atomic program.
The United States accuses Iran of secretly trying to build an atomic bomb under the guise of a civilian nuclear program. But Iran denies this, saying its program is strictly for the generation of electricity. The country ignored an Aug. 31 deadline to cease enrichment.
The Associated Press contributed to this report.