Washington ? Iran, with an assist from Russia and other countries, is developing a long-range missile that would give it the ability to strike NATO countries in Europe, a senior administration official says.

The Shahab-4 missile would initially have a 1,250-mile range but anticipated upgrades would allow it to reach Italy, Germany, Poland, the Czech Republic, Hungary and Greece, according to the official.

The development is worrisome to U.S. officials because Iran has been viewed by the State Department as the world’s most active terrorist country. President Bush has identified Iran among three “axis of evil” members, with Iraq and North Korea.

Despite the emerging capability, an Iranian attack against American allies in Europe is considered highly unlikely because most of these countries maintain normal ties with Tehran, which they believe can help moderate Iran’s behavior.

Older generation Iranian missiles, including the Shahab-3, have shorter ranges and are capable of reaching Israel, Turkey and U.S. troops in Saudi Arabia.

A U.S. defense official said Tuesday the Shahab-3 has a mixed record in tests and isn’t thought to be completely reliable.

Iranian Defense Minister Ali Shamkhani, quoted by Iran’s state-run radio Tuesday, said Iran was taking steps to improve “the destructive power, accuracy and range” of the Shahab-3.

Iran seems increasingly confident about its military prowess. This was apparent when strains developed with Israel after Israel’s interception in January of a shipment of Iranian weapons to Palestinian areas.

At one point, Shamkhani warned that if Israel “carries out any military action against Iran, the response will be beyond the imagination of any Israeli politician.”

Iran’s missile development is proceeding hand-in-hand with efforts to develop nuclear, biological and chemical weapons, U.S. officials say.

The senior official, commenting on condition of anonymity, said Iran’s military buildup cannot be justified as a defense against neighbor and longtime rival Iraq, pointing out that the missiles could fly well beyond Iraq.

In a speech Monday, Undersecretary of State John Bolton highlighted Iran’s progress in developing biological and chemical weapons. He also alluded to its “ongoing interest in nuclear weapons, and its aggressive ballistic missile research, development and flight-testing regimen.”

A CIA report issued this year said Iran has been receiving missile equipment, technology and related expertise from Russia, North Korea and China.

“We’re concerned that Russian technology and expertise is helping Iran to increase the accuracy and distance of their missiles, and that Russian technology and expertise is helping Iran develop fissile material,” the senior official said.