Lebanese national Nizar Zakka was returned to his homeland on Tuesday after being released by Iran where he had been detained since 2015 on charges of spying for the United States.

Iran sentenced Zakka, a Lebanese citizen with permanent U.S. residency, to 10 years in prison and a $4.2 million fine in 2016 after he was found guilty of collaborating against the state.

Zakka, an information technology expert, had been invited to Iran by a government official a year earlier, but then disappeared after attending a conference in Tehran.

The freed Lebanese national was escorted back to his native country by General Security chief Abbas Ibrahim, who headed for Tehran on Sunday to finalize Zakka's release talks.

Following his meeting with Lebanon's President Michel Aoun at the Baabda palace, Zakka declined to elaborate on the circumstances behind his arrest, but denied all charges against him.

"There was no espionage," he said, accusing Iran of "kidnapping him" on false charges and staging a "show trial".

Zakka thanked Aoun, PM Saad Hariri, Foreign Minister Gebran Bassil and Ibrahim for following up on his case throughout his detention period.

"The initiative to free me was born in Lebanon, and today it ends in Lebanon. Therefore, it's a 100% made-in-Lebanon effort," he said.

For his part, Ibrahim affirmed that the case had been solved at the request of President Aoun, adding that the latter's request for his Iranian counterpart Hassan Rouhani to release Zakka was the main catalyst behind this breakthrough while admitting that Hezbollah had also played a role in this case.