WASHINGTON — President Trump’s special envoy for Middle East peace, Jason Greenblatt, will leave the administration, according to a senior Trump official, raising new questions about a long-delayed plan to resolve the Israel-Palestinian conflict.

Mr. Greenblatt has worked closely since early 2017 with Mr. Trump’s son-in-law and senior adviser, Jared Kushner, to design what Mr. Trump has called the “ultimate deal.” But their secretive plan has been delayed for several months, and it is unclear when it will be released — and whether Mr. Greenblatt will be around for the rollout.

Trump administration officials have said that the plan would not be released before Israel’s Sept. 17 election, which would determine the fate of Prime Minister Benjamin Netanyahu, a close Trump ally who has overseen expansionist policies in the occupied West Bank. The vote, if close, could be followed by months of political jockeying to build a governing coalition, which could further delay the plan’s release.

On Thursday, the Trump official would say about the plan only that “the vision is now complete and will be released when appropriate.”