May 12 (UPI) -- The cost of the United States' war against Iran has reached $29 billion since it began on Feb. 29, a top Pentagon official told Congress Tuesday.

Acting Defense Department Comptroller Jules Hurst III told the House Armed Services Committee the estimated cost of the U.S.-Israeli military action against the Islamic regime has increased by $4 billion since an earlier estimate he delivered April 29.

The quickly rising costs reflect higher expenditures for equipment repair and replacement, as well as the "general operational costs" of sustaining the operation in the Persian Gulf and Strait of Hormuz, Hurst said during the hearing on the Defense Department's $1.5 trillion budget request.

The comptroller cautioned that the changing and uncertain nature of President Donald Trump's conflict with Iran makes cost estimates difficult to pin down.

As of Tuesday, Iran, the United States and Israel were locked in a de facto stalemate over efforts to reopen the vital waterway while a fragile cease-fire was in effect. Trump on Sunday brusquely rejected an Iranian response to a preliminary U.S. peace proposal, casting doubt that the conflict would end anytime soon.