But the deal notwithstanding, the US has been pushing for fresh sanctions.
"The US announced a deal with China and Russia for new sanctions right after Turkey and Brazil brokered a deal with Iran," Al Jazeera's Anita Mcnaught said, reporting from Ankara, Turkey's capital.
"Turkey saw that as a slap in the face.
"US officials never believed the Turkish-Brazilian brokered deal would succeed.
"No one [in the US administration] thought Iran was amenible to anything other than sanctions." she said.
The US is unhappy with the deal because it does not include a commitment from Iran to suspend its nuclear enrichment activities.
"There are American officials who think Iran just used the Brazil-Turkey deal to slow down sanctions," our correspondent said.
The controversy over Iran's nuclear programme has dragged on for years with the US and its allies accusing Tehran of seeking to covertly develop atomic weapons. Iran insists its nuclear programme is for generating electricity for civilian use.
Brazil and Turkey have growing ambitions in international affairs. Both countries are non-permanent members of the UN Security council who do not have veto power.
Turkish officials had been in touch with their US counterparts thoughout negotiations with Iran, a Turkish foreign ministry spokesman said. The US and Turkey are strategic allies.
"Hillary Clinton [the US Secretary of State] did not want them [Brazil and Turkey] to fail but she never thought they would suceed. So the US went ahead with the sanctions draft," our correspondent said.
"If Iran signs the letter, then sanctions may not be an option. China might want to give the Brazil-Turkey deal a chance."