US war drill postponed over Iran tensions JERUSALEM - The United States and Israel have postponed their largest-ever military drill to avoid aggravating mounting tensions between Iran and the international community. The missile defense exercise, "Austere Challenge 12," was scheduled for April to improve defense systems and cooperation between U.S. and Israeli forces. NBC's Richard Engel and former CIA officer Bob Baer share the latest about the assassination of a nuclear scientist in Iran. Defense officials told the Associated Press the drill won't take place before the second half of 2012. They spoke on condition of anonymity because they weren't authorized to discuss the decision, which they say was taken on Sunday. Thousands of American and Israeli soldiers were to take part in the exercise, which was designed to test multiple Israeli and U.S. air defense systems against incoming missiles and rockets from places as far away as Iran. Tensions in the region have been raised by a war of words between the U.S. and Iran over the presence of American aircraft carriers in the strategically-imported Strait of Hormuz and the assassination last week of an Iranian nuclear scientist in Tehran. Iranian officials, who maintain that their nuclear research is intended for peaceful purposes, accused Israel and the U.S. of responsibility for the attack. Both denied involvement. The Los Angeles Times reported that the drill was first planned following concerns Israel was preparing an unannounced attack on Iran's nuclear facilities. The paper said the American and U.S. officials were "in close contact on defense matters" but that "Jerusalem and Washington are at odds" over how aggressively to tackle the Iran nuclear issue. U.S. Army Gen. Martin Dempsey, the chairman of the Joint Chiefs of Staff, is scheduled to arrive in Israel this week for talks with his Israeli counterpart, Lt. Gen. Benny Gantz, the Times reported. Amir Mirzaei Hekmati was charged with spying for the CIA. NBC's Ali Arouzi reports. Ron Ben-Yishai, military analyst for Israel news website Ynet, reported that Washington's decision to delay the drill was partly related to financial concerns, noting that the US has cut its defense budget for 2012 by $450 billion dollars.