Donald Trump's Middle East envoy warned on Monday during a visit to the region it would "not be a pretty day" if the hostages held in Gaza were not released before the U.S. President-elect's inauguration.

Steve Witkoff, who will formally take up the position when Trump's administration starts, said he hoped and prayed there would be ceasefire in Gaza between Palestinian militant group Hamas and Israel before Trump takes office on Jan. 20.

"You heard what the president said, they better be released," he said, referring to Trump.

"Listen to what the president has got to say. It's not a pretty day if they're not released," Witkoff added, in response to Reuters questions on the sidelines of a bitcoin conference in UAE capital Abu Dhabi.

President-elect Trump said on social media last week there would be "hell to pay" if the hostages were not released before his inauguration.

Hamas-led militants killed 1,200 people and captured more than 250, including Israeli-American dual nationals, during their Oct. 7, 2023 attack on Israel, according to Israeli tallies.

More than 100 hostages have been freed through negotiations or Israeli military rescue operations. Of the 101 still held in Gaza, roughly half are believed to be alive.

More than 44,700 people have been killed in the assault that Israel launched on Gaza in response, authorities in the Hamas-run territory say. Thousands of others are feared dead under the rubble.

Witkoff earlier spoke to an audience at the Bitcoin conference where those attending paid as much as $9,999 to access special sessions, which are closed to media.