"Relations between the two countries have now reached the level of strategic partnership and China seeks to comprehensively improve relations with Iran," China's Foreign Minister Wang Yi was quoted by Iran's state media as telling his Iranian counterpart Mohammad Javad Zarif.
Wang met President Hassan Rouhani ahead of the signing of the agreement, which is expected to include Chinese investments in key sectors such as energy and infrastructure.
Rouhani voiced appreciation for Beijing's support within Tehran's 2015 nuclear deal with world powers and called for more coronavirus vaccine exports to Iran, the worst-hit country by the pandemic in the Middle East.
"Cooperation between the two countries is very important for the implementation of the nuclear accord and the fulfillment of obligations by European countries," Rouhani said, according to his official website.
"Regarding the coronavirus vaccine, it is necessary to increase cooperation between the two countries, and we want more vaccines from China to be provided."
On Thursday, China's commerce ministry said the country will make efforts to safeguard the Iran nuclear deal and defend the legitimate interests of Sino-Iranian relations.
China's comments came after Reuters reported that Iran has "indirectly" moved record volumes of oil into China in recent months, marked as supplies from other countries, even as China customs data showed that no Iranian oil was imported in the first two months of this year.
US President Joe Biden has sought to revive talks with Iran on the nuclear deal abandoned by former President Donald Trump in 2018, although harsh economic measures remain in place that Tehran insists be lifted before any negotiations resume.
The United States and the other Western powers that signed the 2015 deal appear at odds with Tehran over which side should return to the accord first, making it unlikely that US sanctions which have crippled Iran's economy can be quickly removed.
However, the OPEC member's oil exports climbed in January after a boost in the fourth quarter, despite US sanctions, in a sign that the end of Trump's term as U.S. president may be changing buyer behavior, after a sharp drop in Iranian exports to China and other Asian customers since late 2018.