After months of negotiations and follow-up, the first deals with international petrochemical companies will be finalized by March 2016, managing director of the National Petrochemical Company said in a statement.

"German firms are expected to strike deals with Iran ahead of others," Abbas Sheri-Moqaddam, who is also the oil minister's deputy for petrochemical affairs, told IRNA.

Referring to the fear of foreign companies and banks over violating the sanctions, he said, "They want to be given a guarantee, based on which sanctions will not return easily, as they incurred heavy losses in the past because of the sanctions."

Last week, Sheri-Moqaddam revealed two German companies' intention to invest $12.9 billion (€12 billion) in Iran's post-sanctions petrochemical industry. This comes as the Petrochemical Commercial Company said last week an undisclosed amount of money was deposited to its account in a Spanish bank as part of the outstanding debt related to Iran's petrochemical exports, marking the first of such payments in five years.

Iran and six world powers reached a landmark deal in July that limits Iran's nuclear program in return for an end to the decades-old trade and financial restrictions.

In a major conference last month, Iran signaled that it is ready to open doors to internationals after the lifting of sanctions, planning to attract $70 billion in petrochemical investments in a 10-year timeframe.

Nominal production capacity currently stands at 60 million tons a year, but plans call for doubling the volume by 2021 and raising the output to an ambitious 180 million tons a year by 2025.

Petrochemical products are Iran's second biggest source of income after crude oil. According to reports, petrochemical exports reached 16 million tons worth $10 billion last year.

Analysts say Iran can earn more from natural gas and petrochemical products than it makes from oil, a crucial source of income that has provided the lion’s share of the country’s budget over the past three decades.

But little has been done over the years to expand the number of refineries and there is a lack of finance to build new refineries and export products with higher value added.