WASHINGTON (Reuters) -Any deal between the United States and Iran must include an agreement not to enrich uranium, U.S. special envoy Steve Witkoff said on Sunday, a comment that drew criticism from Tehran.

While Witkoff was reiterating President Donald Trump's position about uranium enrichment, Iran's response was evidence that the two sides have a long way to go to reach any agreement over Iran's nuclear program.

"We have one very, very clear red line, and that is enrichment. We cannot allow even 1% of an enrichment capability," Witkoff said during an interview aired on ABC's "This Week" program. 

Everything begins, from the Trump administration's standpoint, "with a deal that does not include enrichment. We cannot have that. Because enrichment enables weaponization. And we will not allow a bomb to get here," Witkoff said.

The response from Tehran was swift.

"Unrealistic expectations stop negotiations, enrichment in Iran is not something that can be stopped", Iran's semi-official Tasnim news agency cited Iran's foreign minister, Abbas Araqchi, as saying on Sunday.

"I think he is completely at a distance from the reality of the negotiations," Araqchi said of Witkoff, and added that enrichment will continue.

Witkoff said he is optimistic about negotiations and thinks the parties will hold talks again in Europe this week. 

"We hope that it will lead to some real positivity," Witkoff said. 

Araqchi said the date and location of the next round of talks will be announced soon. 

Trump said on Thursday that the United States was getting very close to securing a nuclear deal with Iran, but on Friday said Iran needs to move quickly. Trump told reporters on Friday aboard Air Force One after departing the United Arab Emirates: "They have a proposal. More importantly, they know they have to move quickly or something bad - something bad's going to happen," according to an audio recording of the remarks.

Araqchi said on social media that Tehran had not received a U.S. proposal.

During his first term as president, Trump withdrew the United States from a 2015 deal between Iran and world powers that placed strict limits on Tehran's uranium enrichment activities in exchange for sanctions relief. Trump also reimposed sweeping U.S. sanctions.

(Reporting by Katharine Jackson, Steve Holland and Elwely Elwelly; Editing by Scott Malone and Will Dunham)