Monday's one-day visit by Mullen, the first in a decade by a chairman of the Joint Chiefs of Staff of the U.S. armed forces, came on the heels of last week's U.S. intelligence report that said Iran stopped its attempts to develop a nuclear bomb four years ago.
Israeli officials have disputed the American assessment and remain steadfast that Iran is aggressively pursuing nuclear weapons.
Mullen met Monday with Defense Minister Ehud Barak, Lt. Gen. Gabi Ashkenazi, the military chief of staff, and a string of top generals. The officials, who spoke on condition of anonymity because of the sensitive nature of the talks, said Iran topped the agenda of each of Mullen's meetings.
Iran claims its nuclear development is for peaceful purposes. But Israel maintains that Iran's Islamic regime is still aggressively pursuing nuclear weapons.
The U.S. has said it will continue to push for tougher sanctions against Iran. But Israeli officials, who support that effort, fear the National Intelligence Estimate report will hurt the international efforts to isolate Iran.
Prime Minister Ehud Olmert said Sunday that the U.S. report would not change Israel's view that Iran is continuing to pursue nuclear arms and is developing rockets and enriching uranium.
Mullen also discussed a joint Israeli-U.S. missile defense project during his visit, and was briefed about a mysterious Israeli airstrike against Syria, the defense officials said.
Israel has maintained an almost total silence since the Sept. 6 strike, which Syria said hit an unused military installation. Foreign media reports, some quoting unidentified U.S. officials, have said the strike hit a nuclear facility linked to North Korea. Damascus denies it has an undeclared nuclear program, and North Korea has said it was not involved in any Syrian nuclear project.