Poland's second-biggest oil refiner Lotos is interested in securing a long-term supply deal with Iran once it completes a new coking unit at its Gdansk refinery next year, its chief executive said.

State-run Lotos wants to diversify its imports of oil and gas away from Russia, its largest supplier. It signed an agreement last year with National Iranian Oil Company and the first tankers carrying 2 million barrels of Iranian oil arrived in Poland in mid-August.

It is now in talks to receive another 2 million barrels.

"We are negotiating a supply of heavy oil from Iran," CEO Marcin Jastrzebski told Reuters in an interview authorized for publication on Sunday. "We assume that shipment of two million barrels will reach the (Polish) port of Gdansk at the beginning of May."

Lotos could potentially agree a long-term contract with Iran after it finishes construction of the 2.3-billion zloty ($570 million) coking unit at its Gdansk refinery in 2018, he said.