U.S. and Iranian negotiators have reached an agreement on a 60-day memorandum of understanding to extend the ceasefire and launch negotiations on Iran's nuclear program, but President Trump has yet to give his final approval, two U.S. officials and a regional source involved in the mediation efforts tell Axios. Iran has also not confirmed its acceptance. Why it matters: The signing of the MOU would be the most significant diplomatic breakthrough since the war started, but a final agreement that tackles Trump's nuclear demands would still require further intensive negotiations. "This is an agreement to get everybody to the table. We will work out the details in the negotiations," one of the U.S. officials said Behind the scenes: U.S. officials said terms of the deal were mostly agreed to as of Tuesday, but both sides still needed approval from senior leadership. The U.S. officials claimed the Iranians later came back and said they had the necessary approvals and were prepared to sign.…