Chairman of the Joint Chiefs of Staff Adm. Mike Mullen spoke Tuesday about Iran acquiring a nuclear weapon in rare comments by a US official, acknowledging the possibility that Iran will succeed in acquiring a capability America has long termed unacceptable. "I believe Iran is very focused on developing this capability, and I think when they get it, or should they get it, it will be very destabilizing," Mullen told the Center for Strategic and International Studies Tuesday, in an address on military challenges in the Middle East, sponsored in connection with the embassy of the United Arab Emirates. Mullen said that an attack on Iran would be similarly destabilizing, as in both cases, "there are unintended consequences that are very difficult to predict in a very volatile, highly volatile part of the world." He specifically warned about the Iranian response, indicating that he worried about "the vulnerabilities that regional countries have, who are great friends of ours, their populations" and whether retaliatory violence would spread throughout the region and potentially to other parts of the world. Yet while Mullen backed the Obama administration's approach of dialogue with Iran, he refused to rule out the use of military strikes despite the potential negative effects, saying, "There is a great deal that certainly depends on the dialogue and the engagement, and I think we need to do that with all options remaining on the table, including, certainly, military options." Even so, he expressed concern about the "very narrow space that we have to work towards an objective of not achieving that capability." Estimating that it would be one to three years before Iran developed a nuclear weapon, he warned that "the time window is closing" and that "the clock is ticking." Israel, which has expressed skepticism about the American engagement strategy, has been particularly concerned about Iran running out the clock, and has generally given a shorter timeline for when Iran could be nuclear capable than the US. Mullen noted that Israel saw the issue as an "existential" one, and that he had been in close contact with his counterpart, IDF Chief of General Staff Lt.-Gen. Gabi Ashkenazi, on the subject. He described his Gulf state counterparts, with whom he's also in close touch, as similarly understanding Israel's view that an Iranian bomb is an existential issue, even if they didn't agree with the assessment. "We've worked with our Gulf partners to look at the development of regional defense capability," he pointed out. "They're very committed to that, and expanding that capability over time." Mullen also spoke about his coordination with the Russians, with whom he participated in a summit between US President Barack Obama and Russian President Dmitri Medvedev on Monday. Asked about the concerns Israelis and others have about the planned Russian sales of the sophisticated S-300 defense system to Teheran, which would limit Israel's military edge in any confrontation with Iran, Mullen said that he has raised his concerns with his Russian counterpart in the past. "That particular system is a game-changer in that part of the world," Mullen said. "That's a huge concern because of the potential that it has."