The United States has powerful bombs at the ready in the case of possible military action against Iran and work is under way to bolster their firepower, the air force chief said on Wednesday.
General Norton Schwartz, air force chief of staff, declined to say whether US weapons -- including a 30,000-pound massive ordnance penetrator (MOP) bomb -- could reach nuclear sites in Iran that were concealed or buried deep underground.
"We have an operational capability and you wouldn't want to be there when we used it," said Schwartz, when asked about the MOP bomb.
"Not to say that we can't continue to make improvements and we are," he said.
Amid speculation that a nuclear site dug into the side of a mountain near Qom is beyond the reach of American weapons, Defense Secretary Leon Panetta has acknowledged shortcomings with the giant MOP bomb and said the Pentagon was working to improve the explosive.
"The bottom line is we have a capability but we're not sitting on our hands, we'll continue to improve it over time," Schwartz said.
Asked about recent comments from retired senior officers that some targets in Iran are immune from US air power, Schwartz said: "It goes without saying that strike is about physics. The deeper you go the harder it gets."
But he added that the US arsenal "is not an inconsequential capability."
The former vice chairman of the Joint Chiefs of Staff, retired general James Cartwright, suggested last week that one nuclear facility in Iran could not be taken out in a bombing campaign.
Cartwright appeared to be referring to the Fordo plant built deep inside a mountain near the Shiite shrine city of Qom, some 150 kilometers (90 miles) south of Tehran.
Schwartz also declined to say whether air power would be effective against Iran's nuclear program but said that the outcome of any preemptive attack would depend on the goal of the strike.
"What is the objective? Is it to eliminate, is to delay, is to complicate? I mean what is the national security objective. That is sort of the imminent argument on all of this," he said.
"There's a tendency I think for all of us to get tactical too quickly and worry about weaponeering and things of that nature."
The general's carefully calibrated remarks coincided with a visit to Washington this week by Israel's defense minister, Ehud Barak, amid renewed speculation of a potential Israeli strike on Iran's nuclear program.