The Bush administration has backed away from first use of nuclear weapons against Iran, according to Rep. Edward J. Markey (D-Mass.).

This revolves around a question of whether the United States might use a tactical nuclear device as a bunker buster to destroy deeply buried Iranian nuclear processing facilities.

While the United States and some industrialized nations have criticized Iran for processing nuclear materials, fearing Iran may be developing and producing nuclear weapons, Iranian leaders have denied they are constructing nukes. Rather, they claim the nuclear materials would be used only for electrical power generation.

Some U.S. military officials have said conventional weapons would be unable to destroy these Iranian facilities because they are buried deep underground, and therefore nuclear weapons would be needed to penetrate them.

But now, Markey said, the Bush administration is shifting away from any first use of nuclear weapons against Iran.

He released a letter from Jeffrey T. Bergner, assistant secretary of state for legislative affairs, that came in response to a June 19 letter by Markey and 14 other members of Congress urging Bush to rescind his public threats of a preemptive nuclear strike against Iran. They urged the administration to focus instead on diplomatic solutions to the problem of Iran’s nuclear program.

The State Department letter said, “Both the President and [Secretary of State Condoleezza] Rice have said that the United States is committed to a peaceful, multilateral, diplomatic resolution to this issue.”

The letter also indicated that the Bush administration now is willing to enter into negotiations with Iran should it suspend uranium-enrichment activities.

The letter also noted that the administration was seeking to “build a consensus that sends a strong message to the Iranian regime: it must either work on a solution, or become further isolated from the international community.”

The letter also stated, “We will continue to work with the international community to seek an end to Iran’s efforts to develop weapons of mass destruction, and to counter Iran’s support for terrorism in Lebanon and elsewhere.”