Reuters reported last week that a US-Iranian deal is taking shape in Austria after months of indirect talks to revive a pact the US abandoned in 2018 under then-president Donald Trump.
"The United States must prove its will to lift major sanctions," Raisi said in a joint press conference with Qatari Emir Sheikh Tamim bin Hamad al-Thani in Doha.
"To reach an agreement, guarantees are necessary for negotiations and nuclear issues."
The draft text of the agreement also alluded to other issues, including unfreezing billions of US dollars in Iranian funds in South Korean banks and the release of foreign prisoners held in Iran.
Raisi was more cautious than Iranian foreign ministry spokesman Saeed Khatibzadeh, who said earlier that the Vienna negotiations had made "significant progress".
Khatibzadeh also noted that "nothing is agreed until everything is agreed" in the Vienna talks.
"The remaining issues are the hardest," he told a weekly press briefing.
Khatibzadeh said that Iran's top security body, the Supreme National Security Council, handles the Vienna talks.
It reports directly to Supreme Leader Ayatollah Ali Khamenei, Iran's top authority.
The 2015 deal between Iran and major powers limited the country's enrichment of uranium to make it harder for it to develop material for nuclear weapons, in return for a lifting of international sanctions against Iran.
Iran is ready to swap prisoners with the US, Iran's foreign minister said on Saturday, adding that talks to revive the nuclear deal could succeed "at the earliest possible time" if the US made the necessary political decisions.
Speaking from Doha on the sidelines of a gas conference, Iranian Oil Minister Javad Owji called the sanctions a violation of international law and a threat to global energy security, the Tasnim news agency reported.
Iran has violated some of the deal's nuclear limits since the US withdrew from it and reimposed sanctions under Trump.
Israel, Iran's arch-foe, has been closely watching the Vienna talks.
It is pressing the US about the terms of an emerging Iranian nuclear deal, Israeli officials said on Monday, raising the prospect of a bilateral day-after agreement with the US to address their worries.
While not a party to the talks, Israel has conferred with the US administration in hope of wielding more clout over any revival of the deal with Iran reached over its objections.
