Iran will soon hand a counter-proposal for a nuclear deal to the United States via Oman, Iranian foreign ministry spokesperson Esmaeil Baghaei said on Monday, in response to a U.S. offer that Tehran deems "unacceptable."

Reuters previously reported that Tehran was drafting a negative response to the U.S. proposal which was presented in late May. An Iranian diplomat said the U.S. offer failed to resolve differences over uranium enrichment on Iranian soil, the shipment abroad of Iran's entire stockpile of highly enriched uranium and steps to lift U.S. sanctions.

"The U.S. proposal is not acceptable to us. It was not the result of previous rounds of negotiations. We will present our own proposal to the other side via Oman after it is finalized. This proposal is reasonable, logical, and balanced," Baghaei said.

Baghaei added that there was not yet any detail regarding the date of a sixth round of nuclear talks between Iran and the U.S.

Last week, Iran's Supreme Leader Ayatollah Ali Khamenei dismissed the U.S. proposal as against the country's interests, pledging to continue enrichment.

During his first term in 2018, U.S. President Donald Trump ditched a 2015 nuclear pact between Iran and six powers and reimposed sanctions that have crippled Iran's economy. Iran responded by escalating enrichment far beyond that pact's limits.