A published report says the United States has been flying drones over Iran for almost a year, looking for evidence of nuclear weapons programs and detect weaknesses in air defenses.

In Sunday's editions, The Washington Post  quotes three U.S. officials as saying the U.S. military has been launching the unmanned surveillance flights from Iraq. There has been no U.S. comment on the report.

An Iranian spokesman Sunday again warned the United States not to attack its nuclear facilities. He also rejected a European proposal aimed at restricting Tehran's development of nuclear fuel.

Iran has said in the past it would stop plans to build a heavy water nuclear reactor, which can be used to make nuclear weapons-grade material as well as for nuclear energy.

But Sunday in Tehran, a foreign ministry spokesman said Iran will go forward with the heavy water reactor and will not replace it under any circumstances.