ISTANBUL (Reuters) - Turkish energy company Unit International has reached a $4.2 billion deal with Iran's energy ministry to build seven natural gas power plants there, in what it said was the biggest investment in Iran since the lifting of sanctions.

The power stations, to be built in seven separate regions of Iran, Turkey's eastern neighbor, would have a combined installed capacity of 6,020 megawatts, the company said in a statement.

The United States, European Union and United Nations lifted most sanctions on Iran in January under a deal with world powers whereby Tehran agreed to curbs on its nuclear program.

Turkish companies have seen the move as a major trade and investment opportunity, with the car, clothing, textiles, machinery and chemicals sectors also seen offering potential.

"Unit International has reached a deal with the Iranian Energy Ministry worth some $4.2 billion to build natural gas combined cycle power plants," Unit said, adding the agreement was signed at a ceremony in Tehran on June 1.

Unit International is owned by Unal Aysal, the former chairman of major Istanbul soccer club Galatasaray.

Aysal said that when completed the power plants would meet 10 percent of Iran's energy needs. Construction of the seven plants was planned to begin in the first quarter of 2017.

(Reporting by Asli Kandemir; Writing by Daren Butler; Editing by Hugh Lawson and Susan Fenton)