India plans to invest more than $15.2 billion in Iran to develop key projects including the construction of a petrochemical refinery and a urea plant, said a senior minister.

Besides, the Asian giant is ready to take up full-scale development of Chabahar Port if Tehran offers better terms including cheaper gas, Shipping Minister Nitin Gadkari said on Wednesday.

India is one of the handful countries that continued trade links with Iran, isolated by Western countries against its disputed nuclear programme. New Delhi is Tehran's second biggest oil client after Beijing.

"We are ready to make a huge investment in Iran and this is mainly linked to gas pricing offered by Iran ... Gas price is a crucial issue," Gadkari told a news conference.

Days before the historic nuclear deal between Tehran and the West in July, President Hassan Rouhani offered India a greater role in infrastructure projects including overall development of Chabahar port.

India hopes to take a decision on Iran's latest offer by early October after obtaining reports from other ministries including petroleum, chemical and fertiliser, and steel by Monday, Shipping Secretary Rajive Kumar said.

The port of Chabahar in southeast Iran is central to India's efforts to circumvent arch-rival Pakistan and open up a route to landlocked Afghanistan where it has developed close security ties and economic interests.

The port can also serve as a gateway to the resource-rich countries of Central Asia.

With the easing of sanctions, New Delhi is hoping for a greater and stronger role in Iran's development by taking up projects including building urea and petrochemical projects using gas produced in the Opec-member nation.

Gadkari said building a plant in Iran and importing urea from there to India will help save a part of the Rs800 billion ($12.13 billion) in subsidies and halve the prices for farmers.

"If the gas price is reasonable, then all departments in India can together take up projects in the special economic zone there and investment will be more than Rs1 trillion," he added.-Reuters